I think that admins need to state publicly that merit trding or selling is against the forum rules. At the moment, it seems that the only offence is for a merit source to sell merits.
Argh, no, don't do that! Not all trading of merit is merit trading, so to speak. I've merited people who have merited me because we were participating in a thread where we were all trying to solve various mining issues - I solved one issue and got merited, then the same person that merited me solved another issue so I merited him*. Of course, I freely admit that I was more inclined to merit someone who had merited me - that's just human nature - but said individual did, indeed, post something merit-worthy.
* - I was merited on this post:
https://bitcointalk.org/index.php?topic=2046072.msg30157009#msg30157009 & I merited the person who merited me for this post in the same thread:
https://bitcointalk.org/index.php?topic=2046072.msg30407678#msg30407678