[yeppie]

For automation I would recommend ratelimiting endpoints. I personally tend to use 5 requests per IP/second along with 100 requests/minute as default and then override specific endpoints to e.g. 1 request per IP/hour.

For user input I recommend keeping the first comment submitted by a new account/IP hidden until you/moderators have approved it, after which new comments from that user no longer needs to be approved before they become visible to other users.