Good grief!
I'm with NZLearDriver on this one - this kind of tipping is just bribery and corruption.
The "tip for mediocre service" strategy is particularly bizarre - when I've just paid an FBO for a thousand dollars worth of fuel, a hundred bucks for a plate of sandwiches and a bag of ice, and another hundred bucks for a ride in the van, there is no way that I'm giving them a tip for poor service.