Ditto.

That said, I personally avoid buffets, so I'm hardly an expert, but some wings of my family like buffets and I am occasionally dragged to them (kicking and screaming, of course). I have never seen or heard of tipping anyone except the waiter at the end of the meal when paying (and again, with some wings of my family, the waiters at a buffet do more work than a typical waiter as they have to clear off plates between each of several trips to the buffet. )