As far as I can tell, what is "usual" in Thailand varies from zero, if the divers are European, to 10% or more from Americans. I am not slamming Europeans; just observing that, as far as I can tell, there is no Thai custom of tipping, and to the extent that it happens it is a function of the tipper's custom. If you can fake a Swedish accent a 2% tip will be a pleasant surprise to the crew.
Hahaha funny. I can't fake a Swedish accent but I can do real Slavic (since I am from Slovenia) accent.
However I am not sure what they will think about the gear (bringing pretty much all needed except tanks and weights) as I am diving long hose system and will be slinging pony bottle. Sorry I am not coming with a dive buddy so I am not sure what to expect, thus bringing my own "dive buddy" I also expect that I will have to explain the basic of long hose system to whoever is diving with me (diving from South Siam 3) and what they supposed to do if they are in OOA situation. (Here is my primary unless you are panicking and then I will give you mi pony bottle and tell you to get the hell away from me (well not really but hey
Back to the tipping. I don't really want to "go away with"... I usually tip well in restaurants and elsewhere. I am more concerned that my typical $5/tank unless service is great (more) or bad (less) is going to paint the wrong picture. If $2/tank is for decent service and I get great service I am more then willing to tip $5/tank but I don't want to reward average service more then it is worth. You get the point?
Tipping above average for average service is not helping divers nor the crew. I don't want to reward average above what it is but I am happy to reward outstanding service (and also show that I was not happy with underwhelming service).
So to be even clearer.
US norm is about $5/tank for average service.
So if service was poor I would tip $3/tank for example.
If service was good I would do $7/tank or if service was great $10/tank.
But if in Thailand tip for average service is $2/tank then giving $5/tank would just promote average service and somehow tell it is ok to be just average.
But if average is $3 and I pay $2/tank then one would think they did bad job ...
Makes sense?