To be fair mate, I don't just think it is a filipina thing, although they are particularly good at it.

Yep, you're right on track mate, but they, who think they are particularly good at it, can be found out, and paid back with interest sometimes.
One filipina here in China had the nerve to demand more money 1/2 way through......., when mentally I was not in a position to refuse her, so I agreed.......! But next time round I made her earn it the hard way - thank heaven for capital 'v' - it can tilt the balance in a man's favor to redress a past injustice.