Does anyone agree to give their general contractor a bonus?

[Pat Jackson]

For work that is completed early or above satisfaction in some other manner?  Automatically this doesn't seem like a great idea, and I don't think I'd do so the first few times I worked with someone.

I'm trying to establish a long term relationship with an existing contractor, and wondered if anyone has ever had any luck with bonuses.  I see this as a double edged sword, if the contractor missed their mark perhaps things would go south.  

Just something I've been wondering about enough I thought I'd ask.