Do you mean different twitter accounts with same/very similar tweets? If so, it's not a solid proof. When you have a bunch of non-english speaking guys doing dozens of bounties everyday - of course they'll be copy/pasting.
Plagiarism is bannable offence on this forum, not so much on twitter unfortunately.
I think it's best to follow the money in searching alt accounts/bots. I heard than on one occasion a thousands of bounty-hunting accounts were associated with one ETH address. That's insane.
Is it possible or even a good idea to ban all newbie accounts from participating in any bounties. Make it a site wide rule. If this was added to an increase in merit for jr member to say 3 you may really smash these guys up for good.
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Everything is possible, but forum admins don't run campaigns and do not interfere with their rules. As long as forum rules aren't broken - no one gets banned.
The real problem is that bounty campaigns are paying with their own tokens (created out of thin air) so they don't care too much about fighting bots/alts/spam -as there's no costs to them, so nothing to lose.