No-one ever listens to me  but I will say this anyway .

As far as I am concerned the transaction has two parts:

Phase 1.

1. the seller lists an item for sale

2. the buyer bids, wins and pays for the item

3. end of the first phase - the buyer has fulfilled his/her obligation in the sale. the seller leaves feedback for the buyer - 'fast payment etc etc'

Phase 2:

the item is received by the buyer

1. the item is OK - buyer leaves positive feedback - 'item great ...' - END OF STORY

or

2. the item is not OK the buyer contacts the seller - 'this is broken' etc and negotiations re refund / return of item etc take place. If the buyer is satisfied with the outcome (ie either item is replaced or a refund is given) then the buyer leaves feedback.

This seller retaliation for bad feedback SHOULD NEVER HAPPEN - the seller should have already left feedback for the buyer when the payment was made.

Non-Payment strikes etc should be a totally separate part of the system.