I NEVER let them handle my cards, on the basis of a similar situation to yours...
I was in the local SU bar, doing some tricks on an empty pool table, had a crowd of 5-9 people (mainly nosey gits who were just mooching then vanishing) and one guy said he knew a really good poker based trick - being on a green felt surface it seemed like a good idea, and he sold it quite well to the remainder of the spectators, he did the trick quite well, except he did one thing that all poker players seem to do, bent the living hell out of my cards as he delt them...GRRRRRR

- in trying to stop him it really looked like I was being an annoying spectator and trying to ruin the trick, so I had to just let him carry on, through fear of loosing the crowd, lol
I managed to unbend them, but as it was a new deck (litterally just opened tha night) everytime I shuffled them and held the deck square, it looked like I had a p****e b***k in about 6 places, haahahaa, I ended up just doing some random tricks with them for the rest of the night then put them in my 'use to practice' pile of cards back home...
Yeah, wet cards are a bit of a pain...1 way to solve it / stop it hapening again...just carry an old kitchen towel around with you
Dan