Where do I report fake rep?

I have a guy who was offering free Enclave keys from that German site giveaway in exchange for +rep on his profile. I investigated by contacting the users that left rep for him on his profile and found that they all left +rep for receiving a free Enclave key without stating the rep was for a giveaway so I'd like to know where I should report this. I'm told that it is possible to report it here, the user has already been kicked from the trade group I'm a moderator for.

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