They will come up to you when you are just standing still, talk to you for a few minutes, ask for a drink, and if you say no, then they will ask for a dollar. I never tip in that case since she came up to me and I didn't get anything out of the exchange.
If I do get something, generally a touch/grope, or maybe even some useful piece of information then I will tip them. A flash of skin is borderline and I will only tip if I like what I see as an encouragement for them to continue. But otherwise I don't tip out of courtesy because I don't want to encourage some girls to continue.
I do think that some of the locals really go to town for their dollar and get more than their money's worth. But that dollar may mean a lot more to them than it does to me and they may not be able to afford a visit to the hotel so I would never hold it against them.