Obviously, they'd have to be sluts, so that you can have sex without having to pay, or worry about a relationship. But more than that, they have to be local! I mean, who would want to drive for hours just to have sex? Finally, you won't even have to pay to find them, because why should a useful service charge money?
So basically, they seem to be asking, "are you a cheap and unattractive man who wants convenient and no-strings-attached sex?"
How the hell did I get on that mailing list?