I love that TS4Rent has the option for you to put what position you are, but I don’t know how to go about saying that I’m a complete bottom who is not interested in topping without being crass. Should I just say it outright?

Hmmmm, something honest and straight forward, like "I'm a 100% bottom."   It's perfect.

LOL. It just feels so weird. I added this to my tryst bio yesterday but deleted it because I felt like it was too overt. I’ll just have to get over it because it’s vital information for clients.

"Compatibility notes:
I am 100% bottom only, very much the girl on the receiving end in the bedroom who loves a man in charge. I'm a girl with a little something extra and love receiving pleasure there if that is your fantasy, but of course not required."

It’s just honest and clients appreciate it. Nothing worse than a TS advertising verse and then not really being verse, especially if it’s not the position you prefer.

Not crass. You really should state it unequivocally. Otherwise, a client might want something you are not comfortable with. It’s as much a kindness to him as well as you.