I dont think it is best to have a trust system in which all ratings are based on trades. There are plenty of reasonably legitimate reasons to leave both positive and negative ratings for non-trade related reasons, an attempt to scam is a good example of this.
If you are going to have any influence in the trust system, at a bare minimum, you should have trade experience. Similarly, someone with a lot of positive trust, should have trade experience, maybe not necessarily from the specific ratings they have, but in general, positive ratings should be observations of someone being able to trade and be trusted.
I'm talking more about green ratings rather than red. Still, even a scam attempt is considered trade related. It can have a risked amount, and is not something subjective to the person leaving red trust. But it's obviously good to leave red ratings on behaviour like account trading, shady behaviour and whatnot.
It's not okay to leave green ratings for "valuable contribution" to the forums. When someone is tagged green, imo I want that to mean that the person is trusted with money. Anyone can act "nice".