I don't see that overlap in the social graph implies a high enough chance of discovery. Wouldn't discovery require that members from each group are actually in

I don't see that overlap in the social graph implies a high enough chance of discovery. Wouldn't discovery require that members from each group are actually involved in the same financial transaction (in a way such that people are paying attention to who's involved)? It may well be possible to keep that rare enough for long enough that people try it, and are sufficiently successful to be a problem. (This is certainly not confidence that it wont work, just lack of confidence that it will, pending further reading/experimentation/analysis...)