I think you're already on the right path, doing your homework to avoid the scams and/or ripoffs. The main thing for me is to research reviews and make sure you are dealing with a well reviewed agency or lady who has a good reputation. I'm sure you probably already know by now, one should never have to ask about and discuss money or specific sexual acts.

Never let the situation deviate from the expected plan. By that I mean, do not accept bait and switch  types of scams, or advertising  hourly rates much lower than the rest of the market, results in upselling. These are generally bad signs and not tolerable business practices. The other one to watch out for would be her adding a second provider, the "I can bring my friend along with me for a two girl show"; a "show" is all you'll get.

Hope that helps and addresses some of your question