You can give the girls cash, but a lot of them have a quota either by the bar or the mamasan.
All the girls have their own deals, but sometimes they have to hit 5 drinks per night otherwise they get a penalty which is deducted from their earnings. Plus if the mamasan paid for their trip to HK they have a huge debt to pay off (fake passport, visa, flight). Plus daily expenses deducted from their earnings, like food and housing. So they work those drinks like crazy to pay down that debt.
If she's got a very hawkeye boss they'll have other girls watching if she receives cash and she has to split it with her boss.
Every girl has her own situation or her own deal with whomever got her to the bar, but the main risks are:
#1) They have a drink quota set by someone and they pay a penalty if they don't meet it.
#2) The bar can throw them out if they get pissed at them (for various reasons).
If I've ever really liked a girl and wanted to help, I would buy her a couple rounds and give her some cash and walk away happy I enjoyed my time with her.
That way she made her bosses happy (whomever they are) and she got some cash too.
Just don't fall in love, they all have sad stories that will make you want to do stupid things, or some are playing you to take you for a ride (financially speaking!!
). I could write all night about the sad stories AND about some of the traps guys have fallen into.