The old rule of thumb is not to tip the proprietor. If the bar owner serves you? No tip. If any of his employees do? Tip. Barbershop or salon? Owner cuts your hair? It's so reasonable I personally throw him 5 extra anyway to support his small business, but etiquette says you don't have to. Problem being, most ownership is too ignorant to know the rules.
I spent about a decade working for tips in a few service areas. So many unbelievably cheap scum bags. Glad to be done with that facet of my life. I don't go lower than 15% unless I'm insulted or intentionally ignored. Usually im 20-30% depending on level of service.
Here's an interesting one, Chinese Buffets? They only bring you soda and occasionally clear a dish. I go 10-15%. You?