Well, i checked the four accounts and i would say that your suspicions may be correct, however, it may be also a coincidence for the first 2 accounts +/-.
I saw someone sent 1 smerit then the other return it back in another topic in three minutes. They may be friends or alts. It is up to mods to check but i wouldn't give them a negative trust.
Considering the number of actif users in bitcointalk, trading merit is very low and easy to bust.