My Grandmother was a waitress at an upscale Italian place from the late 50's to the mid 80's. When I was in grade school and high school, I bussed tables on all of the big holidays. A 15% tip was considered the standard and anything more was a bonus. The waitresses made great money there and they always split their tips with the bartenders, bus boys and the dishwashers because that was where a lot of the work was done; clean utensils and glasses, fast clean up and resetting of tables, for quick turnaround on tables, giving the waitress another chance to make more tips.
You know when a larger tip is deserved and you know when it's not. I try to stick around 20% and if they deserve more for being extra attentive, I give it.
I was at an upper scale restaurant in Montana and ordered a filet. The filet came out on the plate with 3 asparagus spears, a dallop of some bullshit hippie mashed potato crap. The filet was about 2x the size of the fork. $48 plus the cost of the sides. I asked for a double bourbon, neat. When the waitress brought my drink and asked how everything was, I asked her why she would serve a steak this small. I sent it back, told her to take it off my bill. Paid for my wife's ribeye, which looked great, and my bourbon. I left no tip because the waitress and the cook knew it was wrong to even platter that gumball size piece of meat. Fuck, it's Montana - they grow beef out here!