not usually, but. . .
As stated earlier, hygiene, friendliness, and an outgoing personality are much more important. However......
Certain things, like a full, unkempt mustache or beard - especially if it smells smokey - can certainly make me reluctant to have prolonged DFK with any gentlemen.
Also, I feel rather uncomfortable when I see clients who are older than 70. It's hard to get into a mutually enjoyable situation for me, if the guy is old enough to be my grandfather! That's my one personal pet peeve - and my agency knows not to book those clients for me. I do feel very bad about making such a restriction, but I think that being honest about it will prevent future difficulties.
Some SP's prefer not to see gentlemen of certain ethnic backgrounds. I don't have these restrictions, but I have heard that it is fairly common.
In short, I think it comes down to how you "click" with any given SP. The best thing a hobbyist can do is to try to establish a bit of a personal connection through a bit of pre-coital chatting (maybe offering a beverage too?) and not answering the door with your pants around your ankles and your palm wrapped around your....
well, you get the idea.
"YMMV" depends on lots of things - but if you do enjoy an experience with an SP, the best compliment to her is to see her again!! Personally, my restrictions do relax a bit more with clients I've known for a long time - but like any smart girl, I won't ever do anything "unsafe"!!!!