Negs and canceled transactions

Some sellers have reported lately that they are protected from negs (actually, any fb) in the case of canceled transactions

Others report the opposite.

Near as I can tell, the blocked cases have all involved:

1. A bidder who did not pay.
2. A bidder who agreed to the cancellation.

More data solicited.
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Well, that didn't take long.
A very quick report of "that's what I did, but I got fb anyway".

And then, it happened to me personally. As a buyer, I had to request cancellation, an accidental buy. No payment. Seller requested the cancellation, I agreed, done. I expected to be blocked from leaving fb, but no. it was still there. A day later, I went ahead and posted all good feedback, which now appears on seller's fb page.