Exchange of merit doesn't really prove anything, especially if the amount of merits is small. Theymos has stated in the past that this would constitute rounding error in the overall scheme of things. It would anyway cease once the smerit handed out to accounts during the roll out of the merit system dries up.
Over time, the cycle of merit exchanges from senders to receivers and back will come to the end because they will finally lose all of their sMerits. And after that point, if they can not contribute to the forum, they will hardly earn more merits. Therefore, they won't have more sMerits to exchange each other.