When I started hiring I was in my 30s and reasonably attractive (I got plenty of sex for free), so I didn't think about whether the provider would be turned on or off by my appearance. However, by the time I reached my 60s, I began to wonder if the pleasure really was mutual or the provider was only going though with the act for the money, and it bothered me enough to eventually stop hiring. It sounds like you are really self-conscious (and uncomfortable) about your own appearance, so as others here have said, it is important that you find a provider that is not going to react in a way that will ruin the experience for you by confirming your fear of rejection. And as several others here have said, the best way to insure that doesn't happen is to be completely upfront about whatever it is in your appearance you think someone would likely be turned off by, so the provider is prepared for it: weight, scars, other kinds of disfigurements, even handicaps. And as has been said here often, cleanliness is the most important issue for many providers. (BTW: don't forget to brush your teeth and use mouthwash.) What you don't want to do is apologize for something after you meet him. If you have prepared him, and he has accepted the appointment, then relax and enjoy yourself.
Note: I don't think that sending him a photo is a good idea. He is the one auditioning for a role, not you.