For full time employees I'm with Mr Pink.
Owners, it depends on how successful I think their business is and how much is charged. (The going rate in Lakewood is ~$25. There's no way I'm giving a tip on top of that)
Shairecroppers, the people I've seen doing it here in Lakewood don't seem to be doing it for a living rather as a side thing. So I tend to not tip