Rather than worry about how much experience they have tickling others, I'd be more concerned with how much experience they have with you - tickling or otherwise. I've been tickled by old pros who have been tickling girls for as long as I've been alive, and I've been someone's first "real" session - and the experiences were frighteningly comparable. I learned real quick not to underestimate someone based on their lack of experience.
What made the sessions so awesome wasn't how much experience the ler had or didn't have, but how well he knew me, the way our personalities matched, the way our senses of humor went together - that's the stuff that makes for an awesome session 😀 Not to mention, trust is a huge factor - and whether someone claims to have tickled one lee or a thousand lees, I'd never get into bondage with someone I didn't know and trust.