I never had this problem. Some write (in English or Thai) in their profile that they are money boys. Others bring it up during chat*. If there is any doubt, I ask "what are you looking for?". If a boy appears on my door without bringing up the issue of money, I assume he comes for fun. That works even in Pattaya.
*The earlier the better. In Myanmar and Cambodia very straightforward, whereas in Thailand you can waste some time chatting until the boy gets to the point. In 2013 I hooked up with a boy in DJ station, went to his room (much closer than my room at that time) and when we were both undressed to our underwear, he told me he is a moneyboy. He was not that good looking that I would pay, so I got dressed, said goodbye, and left.