I have never agreed on the price with a girl before going back to the hotel. Everything has its fixed price. It is like a tuk-tuk trip: they ask Bt 200, you know the price is Bt 100 (or Bt 60 when you are Thai). So I do not bother to ask, and pay Bt 100 on arrival (or Bt 60 when I want to upset the driver). Never had a problem with that.
Same same with a girl: Bt 1,000 is the going LT rate, or Bt 1,500 if she is a stunner. So thatโs what I pay โ on arrival in my room, and never had a problem with that either. Treat them nice, and they will treat you nice. And she will most certainly come back the next night.
One more thought about the moment you pay: most BMโs seem to believe that best you pay the girl the next morning to be sure she stays the whole night. But look at it from her perspective: not only does it seem to her that you do not trust her, but how can she be sure you will pay her the amount that you agreed on? There are numerous stories of men who paid less than agreed claiming that โthe performance was badโ or โhe was drunk and didnโt actually spent time with her, sleeping insteadโ. I believe that by paying her upfront you show you trust her, and she will return that.