On the other hand, the quality of distribution is also difficult to evaluate, because according to theymos, merit is distributed according to each person's thinking, there is no real standard to evaluate it.
While there is no general standard when it comes to merit distribution, there is a general idea of what quality is, and which posts were made without any thought.
I would also think it is more about being active and taking out time to seek out posts to merit. There is no reward for giving out smerits and some choose to simply hoard it. But if a user regularly gives out merits when they come across deserving posts, and actually go in search of such posts, they will be good fits for sources (as you'll be giving a stash which exhausts after a certain amount of time)
Suppose someone wants to become a source of merit, but they don't have much merit to distribute before, so their history of distributing merit seems to be empty.
I would guess this is were being a
somewhat established member comes in. To establish yourself on the forum one would have to be relatively active and if they're good posters they'll pick up merits along the way.