I see what you're getting at.
I have two axes of evaluation for a waiter. One: are they trying hard. Two: do they get it right. If they are trying hard and getting it right, meeting the desires I didn't know I had, they get an exceptional tip (over 20%).
If they get it right, but aren't trying hard, and don't really do more than meet my needs, then they get a good tip: between 15-20%.
If they are trying hard, but not quite getting it right, they also get a good tip, because often the things that aren't right aren't their fault. For example, a slow order may be the kitchen's fault, not the waiter's. And, if the water stops by a few times while I'm twiddling my thumbs to tell me that he's waiting for it too and will bring it to me as soon as it comes out, then he's trying hard.
Likewise, an improperly prepared order (cold food, overdone entree, etc.) isn't held against the waiter, as long as he returns shortly after delivering it (but after I've tried it) to make sure it meets my expectations. A really great waiter, though, will figure out that something isn't right just by looking, and will ask me right away if I'd like to have it sent back, rather than leaving to let me try it on my own. However, if I get something completely different from what I ordered---that's his fault, and it will show in his tip, even if he's "trying hard".
The sins of commission (hovering, etc.) aren't penalized (at least, not much---never below 15%), but aren't rewarded either.
However, if something goes wrong, *and* you don't care, then you can expect that 25-cent tip. I've only done this a handful of times, but when I do, you've really screwed up.