pretty simple, get payment upfront, ask people to leave if they argue.
When i'm in these places i find they tend to have hidden charges and different girls offer different things for their services.
Would be good if there was a set price per service, but i understand these hidden industries are hard to do so.
I tend to just only go for what's offered, if service is bad then i go to a different place. No use arguing about it.

On a side note - Personally in business i hate to deal with Indian people, they tend to negotiate and ask for more than they agree to pay.