Talking to a Canadian guy today who is an international courier based in Bangkok he leaves and comes back 5-6 times a month and always gets a 30 on arrival visa no questions asked, only thing I can think is that he's not returning the same day but still I didn't think this was possible.

It is not important how often one arrives, the criteria is length of stay not to exceed 90 days in any given 180-days-period.