This approach, listing up all transactions of large amount of merits, should be regarded as the first step, as it omits cases such as multiple transactions with e.g. 20 merits between the same users.
It is also helpful to check users who send merits back and forth among particular closed users, which are most likely merit farmers.
To detect such abuses, we need more careful investigations by taking into account not only sent merit amount but also user data.
Another suggestion as what to look for: Accounts that suddenly received the required amount of merit to rank up. Like this one that took only 13 days to get the 150 merit required to go from Full Member to Sr Member.
https://bitcointalk.org/index.php?topic=3052556.msg31426338#msg31426338I have no idea how easy that is to write a script to spot, but it is an obvious giveaway.