This seems more than anything to be a communication problem. It is easy enough to say "Mai aow" or "tam ang" (I'll di it myself). Personally it depends on who is doing the filling for me and what they are filling it with.
You cant really f%ck up beer can you? So please Ms. with the short skirt, fill my glass every time you walk by. Or. "No thanks Mr. Somchai I can do it myself" (see above for Thai translation).
When it comes to whiskey I usually prefer to help my self as they usually add only a tiny amount of whiskey. But with a bit of training (which I dont mind giving the young ladies), lets say 2 glasses worth, they can usually get it right the rest of the night.
And what was this about trying to get money out of you?? I suppose if you have some type of O.C.D that say you must drink every time your glass is filled then they might take advantage of it, but I dont know of any moral issue or rule that says you have to drink just because your glass has been filled..