re: How to deal with women who just use others

I'm tempted to say "just avoid them entirely," but if you can't quite stomach that, my suggestion is to be very realistic and up-front about things.

Make it clear that you realize every interaction the chick has with another human (except, perhaps, for some gigachad that got away) is transactional.

Make it clear that you have the money or whatever it is she wants, and that you're willing to part with it- and make it really clear that you will not be doing so unless sexual favors are forthcoming.

You have to figure out how to make these things clear. Just articulating them verbally may not work, or may even be counterproductive. It's no different from buying a car, and not from a nice premium brand. It's like buying a Mitsubishi. You will need to be on your toes, and to be a-hole about it.