Thailand has not a tipping culture as in the United States for example . The waiters depend on tips to make a livable wage in the US .
I have stopped having a beer at a local foreigners bar on this issue of tipping .
I like to buy a beer as I order them and then the guy serving would throw a plate under my nose with the change . If I never left any change I was often accused of being a cheap charlie .
I asked the guy to forget the tray when i order a beer , That fell on deaf ears .
Now I forget to go there and have a beer in a Thai bar that is far cheaper and no tray thrust at me .
Yes I do tip the bar person often at the Thai bar . Mostly received reluctantly , so i say now its for the ice .