The vast majority of waiters just do their job so I tip based on them getting a decent wage. If I actually get one that does an exceptional job, above what I expect I tip more. I used to have a regular waitress at Buffalo Wild Wings at lunch that would put in our order as soon as she saw my wife and I enter the restaurant and would have drinks for us as soon as we set down. She got a much bigger tip, than what I left the other waitresses that made our lunches take twice as long.
When was the last time you actually tipped someone that did a good job, at a place without a tip line on the receipt? How about someone that just fulfilled their expected job duties?
Tipping is also heavily biased toward white women, with black men making significantly less and has basically nothing to do with quality of service.
ecommons.cornell.edu
Also when no one is watching, most people don't actually tip:
https://ideas.repec.org/p/feb/natura/00680.html I tip every Uber or Taxi driver, because, again, I think they deserve to make a decent wage.
ETA: Yes, in general, if I am paying someone a premium to do work I expect more and am much likely to tip them, than if I think someone underbid a project or otherwise provided a higher value.