I learnt from experience and the easiest way not to have regrets is read a few of the posts from the person you are giving merit to. If they somehow copied a good paragraph from elsewhere or similar nonsense it should be more obvious they are not for real when browsing a few of their posts and comparing. It will take slightly longer but I have to do that as I most often would assume a bias with merit to new people who are higher risk in being legit or not.
Well this meriting criteria/prerequisite would work only for non merit sources who have a few amount of Smerits to give out, thus if a user has around 5-6 Smerits to share, they can have the liberty/time to be this fastidious to ensure their scarce resources (Smerits) is given to the best possible posts. But for a MS who has quite a lot of source merits to give out to users, i don't think they would have the time to check previous posts of the user, they'd basically focus on the very post they are reading and want to merit, it is only when they find something suspicious about it that they can then dig a little bit deeper.
I would also argue as an economy in circulation merit is slightly illiquid, it has the decay factor with some supply but I can well imagine some find themselves in a complete drought and other parts of the forum thats not the case. High variance, its hard to make a system thats not too loose in its standard but also fair to all new and old.
There is no system that is perfect, and the merit system is not, but it has somewhat being the most effective in combating spam in the forum. Smerits do not decay, even if Theymos says he might make it possible to do so in the future, and the only supply (except you're a MS) is 1 merit earned produces 0.5 Smerits.
