Sending or receiving merits is not proof of anything. Do you have actual proof or at least a reasonable suspicion that something is not "normal" here, e.g. merit being sold, or the accounts being alts of each other?

I'm sure you can find greater amounts of merits spent in a shorter period of time for posts that (to you) may seem not deserving. Merit sources and other merit senders are encouraged to try to send out as many merits as possible and put the halved merits back into circulation. In fact it says right there on the merit page: "There is no point in hoarding sMerit; keeping it yourself does not benefit you".