I think it all should go automatically to review with the penalty of gaining a red flag yourself if you abuse the system.

It could work something like this....

Buyer’s gives neg feedback...

eBay sends a warning to the seller to respond as no neg feedback is posted for at least 48 hours

Seller responds to buyer and tries to sort it out.

Emails his side of the story to eBay

.

Independent eBay employer decides on the evidence to accept or not.

This is probably nowhere near a streamlined way to do it but it is a start to a discussion and idea that may work.

Truth is its WAY, WAY too easy to give bad or negative feedback