This has been discussed before, here is the last discussion we had yesterday with LoyceV. If you search you can find a lot of info.
I have suggested it before, but in a 1 Merit per 100 reports (say >95% accurate) ratio. I don't think it's worth making 100 bad posts just to report them, when it's easier to just find 100 bad posts. And if someone reports 1000 posts, I don't mind him reaching Member status. Even if his own posts aren't that good, he'll have a positive net contribution to the forum after 1000 reports.
As I agree with you I see also weakness.
Let us take the ICO pumpers as an example, the bots are creating thousands of comments per day, I try to spare some time to browse and report some profiles in the ANN section,but there is just an disaster, well this is other topic.
As bots are created to post in the threads, seems to be easy to make a bot to report threads.
Here is an example of a report link >
https://bitcointalk.org/index.php?action=reporttm;topic=3292413.27;msg=34433583
Well, you have some cool down time between reports for sure, but I don't think this will stop them as they can adjust the time between reports.
So you have two bots running, one spamming, other reporting. Then you have an extra income when doing the ico pumps from farming menit and selling accounts.
There is an option like captcha to be added for both posting and reporting, but many users already have trouble using it for login so it has to be locally integrated.
Of course there will be real people reporting too, so it's kind of put the shiposters to do some good work, but I don't know what will be the impact of reporting.
This I suggested back in the beginning when the merit was introduced, but as I analyze it a little further I saw a lot of possibilities to cheat the system so...
Here is one idea, merit points as a reward for reporting spam posts/accounts.