We had a "minor" flood a few years ago, and we were under the gun to get it fixed up.
So, we "incentivized" the drywaller, and told him that if he got it done within a certain time, I would pay him a premium.
I guess you could call it a tip, but he got it done within the proscribed timespan.
I've had issues with contractors before not getting the work done within a certain amount of time, and I had struggled with how to mitigate those issues. And we debated the carrot vs stick method.
So far, the carrot has worked much much better than the stick.