Even if you ignore everything else listed if you do just 1 thing you will probably be 90% assured of getting what you pay for, and that is checking references. The best indicator of what someone will do is what they have done in the past.
Insist on references, and not 3, but many. We give out a sheet with about 50 references of past customers. We have nothing to hide and want potential customers to talk to our past customers. Nothing is better than to have past customers brag about us.
Check references, if the contractor can't give you a sheet of them don't consider meeting with that contractor. Only after you have a short list of legitimate contractors can you then evaluate them correctly. If you have crooks thrown in with the ones you are evaluating you can't judge any of them correctly. You won't be able to judge anything correctly. Your price issue of being taken advantage of because of being a woman is a perfect example. You don't know if a price is high if it is high or it is because you are a woman. By narrowing down to a legitimate short list of qualified contractors only then can you then be assured that the pricing you are receiving is not being effected by someone trying to take advantage of a single woman.
I hope that makes sense to you?
Your interaction with SEND IT ALL is a perfect example. Since you have not pre-qualified him ahead of time your only choice is to jump to a conclusion that his costs up front are not legitimate, and that there is some element of him trying to take advantage of you. Now if you had prequalified him before hand you wouldn't even be thinking that way, instead you would be making a logical decision based upon other factors whether you want to pay $150 up front for a measure or not. Without pre-qualifying the issues are too cloudy for a consumer to be able to make good decisions. You are continuously second guessing what somebodies motivations are instead of just being able to focus on the project and getting the best results from the most qualified contractor who will meet your needs.
Good luck. I hope you choose to avoid playing the victim and take control and become an informed consumer.