they can also be said to be MS that make out time out of their busy schedule to give out merits on the forum, or they can also be said to be users who are willing to rummage around quite a lot of shitposts on the forum to give out merits to good posts, etc, etc,
Eh, when I'm browsing bitcointalk my schedule isn't usually that busy--but I'm not the type of merit source who sifts through threads looking for posts to merit (though I will if I come across any). It would drive me nuts if I clicked on random threads simply to check for meritable posts, for the reason you said, which is that the good ones are in a many-layered sandwich of shitposts. I've had enough of that to last a lifetime.
Are there some merits sources who... or do we have a situation where a merit source will stumble on a good post, after meriting the post, the merit source would be tempted to visit the user's post history in search of more quality posts to handout more merits.
~very rare I guess.