I would have thought that for girls like Fatprossie and GlasgowGirl, the solution was easy, just respond to any declarations of love with:
"I'm a married woman" - and they'll leave you alone.
It's all the single girls who have to find the correct form of words so that they can let clients down easily without hurting them.
I'd agree up to a point. A quick "I'm married" should be it, end of story. As you say, the single girl could have a harder time.
Of course, a misty eyed punter may think a married working girl is still "fair game", on the grounds that "well, she's having sex with other men anyway", so hardly committed to that person totally, body and soul, so why not with me?
Now the answer to that may depend on lots of things, I guess, such as the nature of that marriage, openness on the prostitution side of things with the other half and so on. I'm sure it could be a very complicated matter, but I suspect that being married alone would not stop a determined and "loved up" punter!