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Preventing alternate accounts from enrolling in campaigns is stupid. It does not prevent people who secretly use alts and it does not prevent spam. Preventing someone from joining because they have poor post quality is better than preventing someone from joining because they might have poor post quality because of the multiple accounts.
1.) Preventing alternate accounts from enrolling in campaigns is good.
2.) Preventing users with poor post quality from enrolling in campaigns is good.
These things should not be contrasted; they are beautiful when applied simultaneously.
My opinion on alternative accounts: even if the user is a genius and can write great posts from multiple accounts he robs other campaign participants since the payment is intended for the user, not the account.
Bounty campaigns sets limits on paid posts for one purpose: they set some maximum that they are willing to pay one user. Using alternative accounts helps disrupt these plans.