The problem is people are using the trader rating system as a "reputation system".
The system as I understand it is to rate how well the TRANSACTION went. I see your point if there was no transaction, then there should be no feedback.
What people (and I myself I must admit) are doing is using the system to identify flakers.
I think such a system should be in place, but it would have to be moderated and I understand that is allot to ask considering the existing load MODS have to deal with.
I think there should be a way to track if someone wastes your time, and warn off other from a person who jerks chains.
I had a fellow drag payment out for a week then tell me he found a better deal. I was a nice guy, and SPF'd the sale. I gave him negative feedback and a full explanation why, and I still have all the PMs.
Looks like I won't be being a nice guy anymore.