You never can tell till you meet some of these people. Years ago my sister was on "Bob's Full House" (won it too - holiday in Barbados with her husband) and, though happy to get on the show, was expecting Bob Monkhouse to be a smarmy dickhead. She came back totally won over - said he was sharp as a pin, highly professional and really good with the contestants.
I always remember Frank Skinner saying he played in a celebrity cricket match with Jeffrey Archer and how he was absolutely gutted that he turned out to be a really nice bloke!