Hi @JammyDodger , I finally managed to restric the activity in a specific category by eliminating the option of giving likes in it. That way, even though the rest of the stats can go up in that category, the likes need to be received and given can’t - so that avoids users that only use that specific category to scale up trust levels 
BTW, the way to do that is quite simple and has been explained in this other post, in case you want to check: Limiting likes in a specific category
This has made my day and solved all my problems. I hope you find it useful too 