Good ones don’t care. Tell them in advance. The ones that are good will reply with something like ‘it doesn’t matter what you look like, it matters how you behave’. The bad ones will either ignore you or be evasive. Then you’ll know which to book won’t you.
I see all sorts of clients for massage and more escort style work. Some are old, some disabled, some have scars, some are big, some are skinny. It really doesn’t matter except for practical purposes (like will you fit on my massage table, have you got any conditions or injuries I need to know about). As for what you look like, it’s immaterial. I care most about will you turn up, will you be respectful, will you participate and enjoy yourself. Go for it. Anyone who declines your business because of what you look like isn’t a real provider. If you find someone you’re comfortable with you’ll find your confidence grows each time you see him.