I think that a guideline is not a rule, so banning someone for not following guidelines is a bit too much.

Of course the trust system is being spammed and abused, and I don't agree with people giving negative trust to people they don't like or consider spammers. Spamming is bannable, so these people should be reported and it's up to a mod to decide their fate. Trust comments should be given only if you transacted with that person or were a witness of an obvious scam attempt.