Well - here's a vote for overtipping
Folks -
I believe in the Steve Martin line (at least I think it was) from 'My Blue Heaven' - "I overtip EVERYBODY - it's my policy", or words to that effect.
As I get older (49), there's a lot of work I don't want to do, nor do I have time for. I work for a company that offers bonuses, and see the benefit and level of incentive it provides. I think if there's even a hint in the service person's mind that there may be something extra in it for them if they do the job to your satisfaction (or better), the better job they'll do, the happier I'll be, they may be just a bit more courteous, and everybody wins.
I'm bracing for the sticks and stones, but I gave my two guys $50 and a case of beer to split between them. I considered it a very worthwhile investment - they did a great job, couldn't have been nicer, and I was their last gig of the day.