(1) It is said, based on overall post history.
I am not sure what superpower nutildah got to go through 5000+ posts to find a spammer in 24 hours or a week of time.
I guess you talked about 5000+ posts of a user, not the whole forum, and if it is limited to only one user, it's very unnecessarily to check all posts in that user posting history. Open the post history page, check some latest pages (each page has 20 posts), and it's enough to see the average post quality of that user.
In addition, it's possible to use third party tools like BPIP to check merit history, if merited posts are low quality, and merit history is like exchanging, it's another thing.
(2) Based on merits.
For very long time, it has been complained here and there that posts are merited for face-value (known accounts) rather than for the quality of content.
Local board posters get more merits than English posters as same accounts frequent same board(s).
(3) 100+ page or 100+ replies cannot define a spam as the sports or casinos topics are different from other real spam topics.
Agree.
They can create new threads that pointless, just to avoid mega threads while post quality is the same.
Right now sigban is happening in really really UNFAIR way due to lack of proper guideline and warning.
There have been
Guidelines since 2016.
theymos has a
welcome message with a part for writing.
When trying to write quality posts, a lot of people act as though they're writing a book report for school: putting facts that we already know into their own words. Nobody wants to read that, and you will not get merit for it. Moreover, the length of your post and the quality of your English are only minor factors. In trying to write a quality post worthy of merit, you should offer new ideas, personal experiences, or perspectives that other forum users will actually find new and interesting.