It's pretty broad, and many varying opinions regarding abuse on the blockchain. Plagiarism is definitely considered abuse here, not sourcing creative commons images is considered abuse by some, but is a grey area because of variance of opinions.
Mass account creation with the intent to vote farm is widely agreed upon as abuse. Some people will use those accounts to comment a (.) on old posts to hide the activity, then upvote with alts and or/friends who are in on a circle jerk style abuse of this exploitation.
There are witnesses here who are able to link alt accounts. I don't know their techniques for doing so, but posts I've read in the past have indicated that this is an ongoing problem, and new rings are discovered everyday. Of course it happens with the tribes too.
@steemcleaners is one such account which searches for this type of abuse.
@steemflagrewards is another.
The devs from @minnowsupport manage https://steem-engine.com and have linked accounts abusing through use of tribe farming utilizing steem-engine to trade coins.
@jaguar.force Is a skilled team that hunts down and exposes plagiarism.
I'm sure there are some more efforts, these are just the ones that come to mind off the top of my head.
When it comes to tribe abuse, I help on the #weedcash network as an admin. When someone recognizes suspicious or obviously suspicious account activity, we discuss it as a team, and there are different skillsets within the team. If we make a determination that someone is abusing (collectively agreed upon), then either a warning will be issued, or if it is severe abuse to the network, like farming, then a ban from using that tribe token can be implemented to the abusing account(s).
Finding specific posts would take me a while, but you can visit these accounts as references to abuse fighting on the Steem blockchain, and perhaps there will be some posts which outline the specifics you are looking for.
I hope this helps @logiczombie :)