I know you asked the ladies but I thought I would chime in on this. Being a psych student (returned to college, not a young kid), I find this question interesting.
So the reasons to lie,
1 to better the guys performance (so if complemented afterwards it would be true)
2 to insure you are a repeat client (if they WANT to see you again, THAT is a complement)
3 they are new and think they are obligated (you know they are new and know it can be a crap shoot)
Now, the reasons to be honest,
1 they see many men who are clueless and want to encourage those who know how to get it done.
2 the providers are women who enjoy pleasure as much as we do (maybe more in fact), and in general women show appreciation better than we do.
3 just like us, they are not all the same, you might daty one lady and she thinks it sucked, the next might think it was the best she ever had.
Finally, reason not to lie (I like this the best)
1 as you said, you have paid for their time, if they don't really like you or your performance, they lose nothing in staying silent.
2 for every provider there are many of us drooling men, they won't likely run out of us, there is no reason to lie.
3 (and the best) if she lied and said you were the greatest at anything, she would have to remember that for your next visit or get busted in that lie.
Anyway, that's my thoughts, ladies, please put me in my place if need be....no really I'm a sub so would like it!