Here are my copy/paste, probably unorganized thoughts...
When people refer to the feedback system, they want to know if they are going to get screwed over on the product - like after they send payment and then receive nothing or crap. This is pretty much the buyers only defense is to leave negative feedback (depending upon payment type). Now this negative scoring becomes a weaker weapon when negative feedback is about long waits, or you said he said shit before any trasnaction. People going to start getting negative feedback for not being able to come to a price good for both parties in pre-purchase negotiations?...
My point is that there needs to be more clean-cut rules for the iTrader system and i believe that is if you have completed a transaction, trade, or exchange with another forum member, then it is time to provide them with itrader feedback.
You may have had an agreement with a seller and he may have backed out, that sucks, I agree. My point really is that disputes such as that shouldn't be taken into consideration for feedback on itrader. This dispute example is more in the blacker area of the grey area, but it leaves the door wide open for more negative feedback coming from grey-area disputes. Or even positive feedback for worthless pre-purchase shit like "he PM'd me quickly with info. I didn't buy it, but I'll still leave positive feedback."
Main point: iTrader feedback needs to have clear guidelines, a way to eliminate the pre-purchase gray area in all aspects of pre-purchse negotiations. I think the contract point is at time of exchange of goods or payment.
I also agree with Mark, feedback for the pre-transaction is useful. but I don't think we need to mix it up with the post purchase. Maybe that feedback should just be made present in that particular FS thread for public viewing.