Well, I have been modding a fairly large group for the last two years, with over 23,000 members. It’s been a learning experience. Recently, though, I stepped away from the role as an experiment.
I saw that most of the trouble with spam seemed to come from new members. So I stopped approving new members. Simple! The filters in the Admin tools seem effective at keeping out spam, as long as new members are vetted properly. But even for trained eyes it can be difficult to spot the spammers. Bots are easy, typically.
So I proposed to the group owners that they should spend time finding a new way to gain and select members. FB’s tools are effective to a point but spammers, hackers & botters are pretty creative. I suggested it might be a good idea to prequalify the members via a Google Form and/or hide the group entirely from FB searches so that new members have to actively search the group.
But for me, not modding the group’s new members (and still getting it wrong) has been a blessing. I don’t have to worry as much, spam is down. There must be hundreds of new pending members… but it’s not my job now! Phew!