You don’t have to tip, you just normally do. I had one abysmal experience waiting 90 minutes without our waitress even checking in on us, so I didn’t tip.
A "tip" has gone from some extra cash for an unexpectedly great job, to essentially expected.
"Buy beer at our place. Pay us 5 units of currency and we will get you this beer."
There's absolutely zero reason for things to be more complicated than this.