I don't think they can "police" it Paul.
If two guys set up a game and one has agreed to forfeit or lose on purpose, they are still playing the game and WGT is taking a rake.
They would have no idea if a payment had been made privately.
Anyway they have shot themselves in the foot with this one, I've already received a very generous gift from a popular player after I made a cheeky request to CIB about gifting (I'm still open to that gift Chris, if you so wish ;-p), mostly because he's a decent person, but also because he basically said 'he now had no goal to aim for and his credits were virtually worthless to him....and he was also playing a lot less because of the way WGT is becoming'.
Now I can't imagine he's the only player with a good few credits to feel the same way, take CIB for example. And if I was in that position, I would sooner another player make use of them rather that WGT have them back.