So, lets be honest. A lot of home owners do their own wiring. To be fair, a home electrical system isn't too complicated when you know what you're doing. The problem is that there are actually many different ways to wire a house that will WORK but aren't necessarily SAFE. I've seen a lot of situations where the home gamer gets the lights to flick on and off and calls it good only to find out that their home is wildly unsafe or even a fire hazard.
So I'd like to address the second most common electrical mistake I find outside of the electrical panel itself and that's reversed polarity at an outlet. This is one of those things that you would never know is wrong if you're just plugging in the toaster but electrical systems are designed to make them as safe as possible and reversing the polarity on an outlet is one of those common mistakes that just needs to get taken care of. Luckily its an easy fix but lets talk a little about what this actually is and why you don't want it lurking in your home.
First off, I am not a licensed electrician so, to appease the lawyer gods, don't implement any of the information here without first getting a licensed electrician's say so and if you're in an area where you can't do your own electrical work, don't do that either. As a matter of fact, if you're in an area where regulation has rendered your ability to take care of your own house and home moot, I'd recommend not going out into public unless fully padded. You get the point.
Now, there's a lot of electrician jargon and shorthand that makes their work faster. Most people don't know any of that so I'll do my best to explain things in layman terms. If you're an electrical engineer and want to get into the nitty gritty about grounded vs. grounding, neutral balancing, split phases and the like; this isn't for you. Here we're talking about Homer Simpson level mistakes.
Your home runs on AC or Alternating Current which flows in both directions through the circuit but for our purposes here, we should think of electricity flowing in one direction from the un-grounded or "Hot" conductor (commonly black or red wire) to the grounded or "Neutral" conductor (commonly white). There is another wire that should only ever be used as a safety and that is the bare copper ground.
Every switch or outlet in your home is like a gate that opens when you connect the contacts or plug in that hair dryer. This allows electricity to flow from the un-grounded black Hot wire to the Neutral. When we "ground" our circuit what we are really saying is that we created a path for electricity to complete its circuit and return to its source. Electricity in a circuit will always try to return to its source and there are three ways to do that from the Hot side. Through the neutral wire (the way its supposed to), through the grounding wire (the way it can go if electricity escapes the Hot side but can't return through the neutral), or though you if you're touching the Hot wire and you happen to be "grounded". That means you're in between where the electricity is coming from and where it want's to go. Back to its source. Because this can happen through the actual earthen ground is why that whole ground thing got its name. But I digress.
So, reversed polarity is when the side of an outlet that is supposed to send electricity to the appliance is connected to the the returning wire and vice versa for the other side. As mentioned, your home runs on AC current so things will still work but for our purposes the business end of the circuit, the Hot side, will be feeding whatever you plug into the outlet from the Neutral side and this can lead to safety problems.
Say you're making an English muffin for breakfast and the dang thing gets stuck. You flip the switch off and stick a fork in it but the internal toaster switch cuts power from what it thinks is the Hot side of the circuit but now power is coming in from the neutral side so the toaster is still energized. You've forgotten your bunny slippers so you're bare feet make great conductors and you get a full 20 Amps of Zeus's solution to thing's Zeus doesn't like. Breakfast ruined.
Now, having survived your hot breakfast, you go to change that light bulb that has been bothering you. You ascend the ladder with some pride seeing as you're still a little wobbly from your previous shock but your electron induced state causes you to touch the threads of the light bulb socket. Normally, this is Neutral but today, its wired Hot and Tesla's angry pixies go charging through you and that aluminum ladder to get that circuit completed.
I'm having a little fun with the scenario but, in all reality, its a pretty serious matter. This is a simple mistake that can be dangerous and often years of use with no incidents lead to a false sense that everything's OK. Often when a home turns over to new owners, its because someone has young kids so I inspect every home with the worst case in mind. I don't mess around with safety but, I pay particular attention to things that could hurt toddlers, young children and elderly people.
So what can you do? Go to any Home Depot or Lowes and pick up an outlet tester. You can get a pretty good one for around 10 or 15 bucks that will be 99% effective. These aren't foolproof and there are ways to trick them but aside from opening up the outlet, they do a pretty good job. If you do find reversed polarity outlets get an electrician involved. Its a simple fix that doesn't require any additional parts and the labor shouldn't be much more than a trip charge. If they're taking more than a couple minutes per outlet, they're slow rolling it. All that is required is to swap the Hot and Neutral wires to the receptacle.

What to know first
Understanding your home inspection should start with the question of why you would want one. The concise reason is that the home inspection is your opportunity to examine the property under contract before the contract is executed e.g. you own it and any problems that come along with it. This is the legal concept of "Caveat Emptor" or that it is the responsibility of the BUYER to know and understand what they are purchasing.
If you think about it, most home owners, unlike most sellers of goods or services, are not knowledgeable about the thing the home they are selling. There is a document called the "Sellers disclosure" where they list any issues that they have knowledge of and this satisfies the expectation that they are selling the property honestly to the best of their ability. You could accept this as good enough but you would have no recourse if a serious issue rears its ugly head further down the line. An inspector is typically the best option as you have one generalist examining the property in total and if there are issues that need further attention from say a structural engineer your inspector will be able to determine that and get you on the right track. This has been formalized in real estate law and is now the standard across the country. ​
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What is a home inspection?
A visual examination of the property under contract. What does that mean? Every home inspection is governed by the Maryland or Delaware SOP or "Standards Of Practice". You will get directed to a copy of this before every inspection and I recommend that you read it. This will list the mandatory elements of a home inspection. This is the minimum standard and over the years, we have incorporated much more detail and use a variety of different tools to create a more thorough and useful inspection. More on that later. 
This gets a bit into the legalese so I am required to say that we are not Lawyers and the only legal advice you should take is from someone who is a member of your state's BAR. We are not Lawyers and that's great because they live a unique kind of white collar office purgatory that seems just awful.
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​To understand where your inspection report comes in you have to understand the definition of a representation. The seller of a good "represents" that good to the best of their ability and in good faith whether that is a birdhouse or a real house. Your inspection report is your primary tool to determine if the representations made by the seller that are contained in your purchase agreement are being met. Its also an opportunity to have a competent person examine the real estate being put up for sale since a home owner may not necessarily be able to make a correct representation of their home or understand how to disclose problems because they are not experts in building science.

For instance, if the seller is representing that the home is move in ready with no defects and no issues are listed in the sellers disclosure, your inspection report is your means to bring issues we have discovered with the property to the sellers attention and between both parties and the parties agents, determine a fair outcome. You may also decide that a home does not meet your expectations and that the sellers are not willing to address your concerns which, unfortunately, sometimes happens. In these rare instances, your inspection clause will govern weather or not you are able to walk away form the purchase with no penalty. Remember, legally, it is always the BUYERS responsibility to know what they are buying (Caveat Emptor). In the case of real estate, this makes it especially important to have someone with knowledge and experience do a thorough inspection. 
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How to prepare for a home inspection
There are a few good rules of thumb to go by prior to inspection day.
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1. Get a good point of contact for your agent and give that information to the inspector. This helps with coordination and access to the property as well as passing along information to the seller such as reminders to remove obstructions from inspect-able areas and to make sure that any animals are out of the house. Remember, sellers are going through the same marathon as you and may forget that they are obligated to make all areas accessible to the inspector. The terms of an inspection clause are typically worded as a "satisfactory" inspection. If all the moving boxes are stacked around the electrical panel and furnace, we won't be able to examine them and determine if they are in satisfactory working order.
2. Read the SOP and ask for a sample report so that you are familiar with what to expect in your inspection and forward a copy of the Sellers Disclosure to your inspector if available. Remember, a home owner may disclose only what are symptoms of a problem to an untrained eye. 3 hours is actually not a lot of time to go over all aspects of a home and having a copy of this document allows us to pay special attention to any areas where the disclosure lists symptoms of something that may need a closer look. 
3. On inspection day, touch base with your inspector to determine when to show up. For most clients, I recommend showing up around 2 1/2 hours into the inspection. This does two things. It makes the best use of your time and allows the inspector to maximize his or her attention on the task at hand. There are clients who like to be there for the entire inspections, follow along and ask questions. This is perfectly fine but it may lengthen the time that it takes to get the inspection complete. Arriving towards the end allows the inspector to wrap up any major issues in one on site conference and at this point we are able to determine if one issue is being exacerbated or impacting another. 

What will be on my report?
Your report will cover every major system, area and component that can be visually examined or accessed safely. These include:

Lots
Roof
Exterior
Garage
Basement/Foundation/Crawlspace
Structure
Bathrooms
Bedrooms
Living Areas
Laundry
Attic
Electrical
Air Conditioning
Heating
Plumbing

Using Your Report
Once you have your report, what should you do? First, carefully read the report in its entirety. There is a lot of important information contained in it and it can be very beneficial to go over everything, not just the defects. Your report will list issues that we have found from simple deferred maintenance to serious safety defects. Its important to view the comments in context. Some issues are simple fixes or can be addressed at the home owner level. Where defects are concerned, consult carefully with your realtor to determine what is important to get addressed and what wear and tear is expected with the general condition of the home. This is your opportunity to get any of these addressed because once you walk away from the closing table you have bought the home and any issues that it contains. Do contact your inspector with any additional questions, concerns or if you would just like to follow up.  We're always happy to help

​Caveat Emptor!
​Paul