Done it. It's the proverbial crapshoot. There is almost never any way to know how ticklish they are before you pay. I had one duo who let me pre-screen them before paying (and the one girl was a immense amount of fun). Often, it's pretty mediocre results. But sometimes you find one that is fantastic.
The secret is, don't assume that because one is awful they all are. You may have to spend a pretty fair amount of dough to find the good uns but they're there. And don't pick only one. Just cause what you want to do may be legal in your jurisdiction, remember, that most of their clients seek less legal fare. So you never know when one is gonna get busted. Make sure you have back-ups. And best advice...keep it to tickling, and pass on all the sexual favors.
Christopher