Do it! And be generous. None of this 5 or 10% as might be usual in the West. Try 25%-50% or more. If you paid $10 for a massage, maybe $3-5 is good if you enjoyed your massage. Even if you didn’t, at least give them a little extra. If you had problems with the massage (such as annoyance at their texting during massage), let them know. And perhaps tell them that they would have gotten a much bigger tip if they had concentrated on you and given you a two-handed massage instead of one on their cellphone and one lazily rubbing you.
Asian massages are cheap and a bit of tip isn’t going to kill you and it will mean a great deal to the masseuse.
Out of a 7-15 dollar massage, the masseuse might only receive a dollar, and in some cases, nothing at all. They may have some room and board arrangement with the boss where they get free accommodation, some basic food, and a small salary, perhaps $40 to $150 a month. Your two dollar tip is a big plus for them.
Masseuses commonly make just enough to survive and often have to support a family. Tips go a long way!
Small gifts are always appreciated, as well, such as luxury food treats like a chocolate bar or a mango, for instance. I would bring a roasted fish on a stick to one woman and she loved it.
If you’re a good tipper and a nice person, repeat visits are sure to be very rewarding!