I hate paying up front. I have almost always been disappointed when I paid first. There is no incentive to do a good job when they already have the money. I usually still pay the base rate when service isn't good but no tip. I have paid less, like about half the original price, on a couple of occasions when things went south early on in the session and I left early. For example, there was an escort who "promised the world" in our email correspondence but only gave me about 30 seconds of service before saying he needed to use the bathroom to properly clean himself (which he should have done before, of course). He came back in a few minutes but said he couldn't perform anymore - only light stuff for the rest of the session. I got dressed, gave him a little money and left with him yelling at me for full payment. I was probably there for only 15-20 minutes at most and the problem was on his end, not mine. (If the problem was ever on my end, I would pay in full though.)