I doubt a campaign of this size is even manageable. Pajeets are coming.....
The first step would be to set a Merit requirement: if someone haven't earned at least 10 Merit in over a year, he has no business in any campaign. If someone bought 10 Merit for a bad post, that easily disqualifies him too. YoBit could for instance use
my list of earned Merit to reject anyone who doesn't meet a certain minimum.
That might help a bit but we've already seen plenty of merit networks helping accounts to rank up/receive more merit.