That's thing, there are no official rules for trading merit with your alts (or friends,)
I know it's nitpicking but this (emphasis mine) is what I would consider a "rule" against meriting alts, along with the obvious ethical concerns:
You get merit points when someone sends you some for one of your posts. Additionally, when someone sends you merit points, half of those points can be sent by you to other people.
That's not nitpicking, it's a valid point. It's obvious to me (and probably most) the merit system is intended to reward folks for contributing to the forum and making it a better place for all.
Merit shouldn't be used to reward yourself, or help your friends rank up. And I think those who are blatantly misusing it should be tagged. I'm just not convinced that's the case in this particular situation.