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
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"
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?