I customarily tip 20% to tipped workers. Its dependent on people not being cheap assholes. Which most are unless drunk. I think the minimum tipped hourly wage is 2.15 or something. Its dumb.
I used to deliver ? in my 20's. So many shifts where a majority didn't tip. Got to the point I was happy with at least a dollar. The most hated were the people who would give a card with a religious note inside minus the tip. They should get a regular wage period.