I ran into this situation at Drais, and after-hours spot in Vegas. Most of the spots are good about not letting these chicks in, but Drais works out a little arrangement with them I think. They aren't obvious either - they dress to blend in. They come to your table and make nice and hang out, and the better ones make it seem like they're average chicks just being friendly. When you're ready to bounce, they make their move. If you balk, they've already drank for free on your dime. One dude was actually are real pimp, with a couple of his bitches with him. He wasn't even trying to hide it, and was openly trying to solicit business. Crazy.
"The best kind of pride is that which compels a man to do his best when no one is watching."