What if the number of posts you are allowed is tied to the length of time you have been registered on the site? You could be upfront about it, say for the first week after you join you may post twice the number of days you have been a member, then the restriction is lifted. That won't stop trolls, but I was wondering if it would put a damper on the chinese spammers. But then, I don't know whether they have an attention span that long... But I have noticed that new members tend to dip a toe before jumping in full force, and it wouldn't have discouraged me.
No need for a reply on this, maybe it's been flown and had holes poked in it before.
Intermountain (Cascades and Coast range) oak savannah, 550 - 600 ft elevation. USDA zone 7a. Arid summers, soggy winters