way back in my bartending days I would try to serve all equally at first, that said, those that tipped WHILE they were drinking rather than waiting until the end received a better pour, a free round, I'd make sure to get their repeat order ahead of others, etc etc.

The owners of the bars I worked at would have heart attacks at first but then realized most of the cheap a$$ went someplace else & the groups &/or "heavy users" would usually come back, thus more $$ for the owner.

If a drink was $5 and one normally tipped a $1, if happy was around and the drink is now $2.50, if someone tipped $.25 or $.50, you can guess how their service from me would go.:D