What I am trying to implement into campaigns I manage is users must have merits to join. I currently am allowing users without merits to join(partially), but have started paying higher rates to users with merits. Eventually I will make it a requirement to have merits in order to join campaigns I manage. I would also like to go as far as you must earn merits each week to stay in a campaign.
If all managers do something like I mentioned above, then eventually these shit accounts are phased out and not making any money anymore rendering their accounts useless. With the merit system being fairly new, I can't go full fledged merit crazy on everyone yet. Gotta give ppl a little time to earn some.
Sadly this just often leads to more abuse as we have already seen with a group of people on one of your campaigns just trading merit between themselves to both get on to your campaign and get the bonuses. Whatever systems we put in place people will just try find ways round it if they can and those with multiple accounts can often do so quite easily (and the ones that don't are often just engaging in merit for merit trades). I still think the only way we're going to combat abuse is to just remove signatures altogether and make people pay a hefty sum to get one. Really can't see many people shelling out $500+ on more than their one or two accounts.