There is no question, if you are inspecting property, clothing is mandatory. But what kind of clothing?
I'm a Real Estate Broker and there is a certain level of dress that is expected. That being said, if I am listing a farm, I will dress somewhat differently to climb through the barns and walk the property then I would if I was listing a down-town condo. For starters, if I showed up on a horse farm wearing heels and my best power suit, it's unlikely I would get the listing. However, if I showed up in dressy jeans, with sensible shoes and my Wellies in the trunk, I would score all kinds of marks with the Seller. The other consideration is whether the clients have met me before. I am much more likely to dress higher on the scale the first time I meet a prospective client. Once we've met, I may be a little more casual, but never to the point of casual jeans, cut-offs, shorts or sweats of any kind. They are simply not professional.
As a Home Inspector, you only have one chance to make an impression on the client. You may only be meeting them once. So what do real estate professionals and the public expect. Don't worry, it's not a power suit. Well, maybe it is for you.
Your Head
Let's start from the top down. Hats are not in the picture. Unless it has the company logo on it, forget it. The only time it's acceptable is if you are wearing a rain hat (when it's raining) or a tuque when it's cold. Your hair should be neatly trimmed and short. Sorry to say it, but long hair on a male is attractive but does not instill confidence unless it's confidence in your ability to handle a Harley. There have been studies that men with beards and moustaches are considered to be less trustworthy. How attached are you to your facial hair? I'm not telling you to shave it, but you might want to consider it. Sadly, your handlebar may affect your business.
The Top Half
In summer a short sleeve, button up shirt or a golf shirt with or without the company logo is fine. If you sweat a lot or are in a hot climate, do what you can to mitigate sweat stains. In the winter or colder weather, a jacket with or without logo is fine. During the winter a long sleeve button up shirt will do you well.
The Bottom Half
Stay away from jeans. Make sure that any pants that you do buy fit you properly. The last thing you want is to become the typical contract-guy with plumber's butt. If you don't know what that is, look it up on the Internet. Then get a friend, spouse or relative to tell you if you've got it. It's not professional or attractive and will make you the butt of the joke. Cotton pants are your best friend. Darker colors always come across as more professional looking. Corduroys are fine too. Work pants are more associated with Contractors. You aren't a contractor. You are a professional business owner. You need to make sure you dress like one.
Other
You may want some coveralls for those dirty basements, attics and crawls. Why wreck your good clothes when you can put on some coveralls. Make sure they are as clean as possible, but coveralls that look like they've seen some action are not usually a problem.
In General
Make sure all your clothing is clean and neat with no stains, rips or tears. If you have a vehicle with your company name on it, remember that wherever you go, potential clients are looking at you. Dress as if you are on display, because you are. Sweats are for the gym or for hard physical exercise. That's the only thing they are for. They are not for work outside the home, or shopping, or any other public place. Don't wear them anywhere, ever.