but it's not exactly illegal so who cares right? Unless they are cheating campaigns it means nothing really.
If the user is a merit source then it is prohibited to exchange merits between alts and some have even lost their merit source status for doing that.
And the user appears to be a merit source based on sent and received merit numbers.

If OP has any valid evidence to claim the user is exchanging merits between his alt accounts then he can contact theymos and ask for further investigation.