Why are all these preventive methods of protection? Just deprive these sections of the ability to hide their fraud. Instead, the community is trying to warn users with this multi-step jumble of tips. Just remove self-moderation from these sections and it will be a million times more effective than all these tons of explanations on how to behave in a self-moderated topic.
The flipside is that legitimate trade topics can be easily flooded by competitor sockpuppets. Self moderated trade topics have a use case but as many other things on this forum this feature is abused by shitheads (see korner LOL) and it's being allowed due to some misguided equal opportunity free speech fallacies.
Perhaps self-mod privileges should be tied to rank or earned merit but that would have disadvantages as well.