Very likely this is about XinXan is sending merits to his alt accounts, or he is selling merits. I read somewhere that the average price of 1 merit on black market is around $5 or more, so it doesn't surprise me that there are such suspicious transactions.

I think there is very little that can be done, everyone is almost completely free to give his merits to any post, no matter what the post is about. I think this kind of thing primarily discourages some users who have a very good post/s but no one rewards them with even 1 merit.