Then I put a negative trust on his profile but he still doesn't stop.
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Then you should deal this with Reputation section where all those users who are trying to cheat will get more negative trust.There someone threads exists with the same kind of scammers so use the search to find that thread or create one for yourself..his manager must take their responsibility for that. His manager has already hired for that thing and it's his job to clean the campaign from the scammers.