"ATP" writes:

I guess I can leave feedback on the latest one because the auction actually
ended, I was sent an invoice, etc..

In that case, you *should* complain to ebay. Ebay's (biased) rules say
that a seller can cancel an ongoing auction at any time for any reason
before it ends. But once it *has* ended on time (or ended early, if the
seller didn't cancel all bids), then there is a winner and the seller is
obligated to complete the transaction.

The seller is not supposed to be able to decide after the auction end
that they don't want to sell the item. That deserves a negative, plus a
complaint.

(And if the seller negs you in retaliation, you can post a response to
that negative. Just state that the seller refused to complete the
transaction).

Dave