I've had to deal with a couple of WoP incidents recently, so lets clear up a few things
1)WoPs are not supported by admin/mod/event team/operators
2)Don't ask one of them to referee for you -- if they say yes, it is either a)they dont know to not support it or b)they are doing so as players in the community, not representatives of UR
If you do decide to WoP anyway
1)Create an event that clearly shows it is a WoP match -- not a practice match or whatever else.
2)Take screen shots of the match history -- you may need it to show your referee
3)Pick a responsible middleman who will take possession of whatever cards/clintz you are betting
4)DO NOT play the matches without confirming with the middleman that everything is good and he has bets from both sides
5)As a middleman, under no circumstances give out cards without confirming the results of the WoP
6)If things go wrong, that is for the 3 people to sort out -- which is what makes picking the right middleman even more important -- i suggest using a visible member of the community with a good repuation
So i'll repeat, WoPs are not supported. Participate in them at your own risk.