If the hamster is moving in the same cage each time, then he's effectively taking his territory with him, which reduces the stress for him. As far as hammy is concerned he's staying put, it's the people that are moving. However, all those excited little kiddies grabbing him might not be much fun, but then I've never approved of pets for sticky handed children. I like the idea of getting pets too heavy for children to pick up. Maybe he's got a couple of really laid back hamsters that he sends out on the away missions.
When I've hamster sat for other people, the little critter didn't really seem too bothered, as long as it got fed, but then I wasn't a little kiddy and I wasn't grabbing at it all the time. I dunno. I think it's a better idea to let a person try a pet out and bring it back, no questions asked than to sell them a hamster, have the child get bored, and the animal gets left in a dirty cage with intermittent feedings. But I'm not sure I like it if it's always the same two hamsters and they never get a loving home of their own.