First thing, the “info” you see in these places are very likely not the reality of the situation. Lots of rumors, hearsay, speculation, etc.
So take all this with a grain of salt. But onto the rest of your post:
Advertising your crafting skills is allowed in Trade chat, but it’s still subject to spamming rules. If someone thinks another person is posting too often, they are allowed to report them for spam.
Blizzard does not require players to be “right” when reporting. People are supposed to report the behavior to Blizzard, who will then investigate the situation.
Again, players are allowed to report what they feel are violations. Their intent is irrelevant. Blizzard is the sole arbiter of what is a violation. Someone can report a player a million times, and if there is no rules violation, then nothing comes from it.
Now when discussing squelches, there can be a threshold where a squelch is applied. If Blizzard sees a pattern of the same group causing squelches, then they can take action against them. But this is a pretty rare situation, as the threshold to reach a squelch is relatively high, and it’s unlikely that one group can reach that threshold themselves. Not impossible, but very unlikely.
No. Players are not banned because of “abuse”. If they are suspended/banned, then Blizzard found that they were violating the rules. No player can apply an actual suspension or ban to another player. The only thing that another player (group of players) can effect is a squelch.
If people are getting suspension and bans for spamming, then the solution is to stop spamming. Again, this is not a player squabble. It’s Blizzard saying to stop it.