I know we've had this deiscrussiption before, but ...
There aren't any reports from you telling us which posts you believe are suspicious. Even a single report, with a link to some of the posts you are concerned about, is all that we need to look to see if this is really happening.
And I'm not really looking forward to the idea of having to actually read some of those threads to see if I can find anything rule breaking or figure out what pattern you are seeing.
So - please report it. All you have to do is make a single report with a couple links to some of the posts you think are suspicious.