I rarely drink at beer bars, but go (used to go?) to gogo bars. When I invite a boy to sit with me, I will buy him a drink and check skin temperature and make some small talk. That might take 15 minutes and he will get 100 Baht.

Years ago, I pondered tipping 50 Baht for that, but decided against it.

If a boy sits long time (1 hour) with me and is entertaining, he might get 200 Baht. But that's the exception, only if I can't decide where to go next, that I stay that long in a bar.