Yeah, Ebay needs some serious overhauls - but instead they seem to just be focused on periodic increases in listing costs and the addition of annoying trivial "features"
Feedback blackmail is rampant and Ebay loves it - they have a deal with SquareTrade, a feedback moderation service that charges to help you get rid of bad feedback. If Ebay wasn't so obsessed with being evil, they would institute a time window for sellers to leave feedback - the buyer should be required to indicate payment sent date and depending on how it was sent the clock would start ticking. Seller's motivation would be to receive reciprocal feedback, but buyer would not have to fear being honest. Usually the buyers end of the relationship is all settled after having made payment- in the rare instance that the buyer manages to piss the seller off enough, the seller could append comments to his original feedback "ewwhh, I didn't mean A++++ at all, more like F--, I'm really angry! grr." but this would not affect the buyer's rating. I personally don't hesitate to give negative feedback to anyone whether I have received feedback from them or not - but I consider this nothing more than an act of goodwill to alert future buyers - it certainly does me no good to be honest - I just get revenge feedback - usually followed by an offer to mutually withdrawal - I then feel obliged to waste a half hour explicitly explaining to these folks what spineless scumbags they are.