Unfortunately, it is very difficult / impossible for me to prove a negative (i.e. that I no longer own the items in question).
My 16 BTC sale of a silver half was escrowed by Blazed, who publicly verified the trade in Chainsaw's thread. I could tell you that the coins are still in escrow while the buyer verifies the PGP docs, but we could both be lying. The buyer could come forward but all three of us could be lying.
I did not sell this set for 35 BTC (when does firm mean firm?) but I did sell it for more than 30. Quickseller offered 24.5 which I declined. However, I could be lying about both of these things too. Quickseller could perhaps verify that he offered me 24.5, but he could also be lying about that. I could show the transaction where the buyer paid for the items but I could be lying about that.
Three of the coins in this set were purchased from smoothie, so you could also ask him whether he sold me any coins recently. I did pay him 0.5 btc for PGP docs for each of three coins (1.5 btc total) in this set, so technically smoothie was the first recipient of cash-for-PGP-docs. But smoothie could be lying about selling me the coins and docs.
REALLY, the only way to know with certainty that I sold the items:
1) If the buyers share photographs of their items (why would they?)... but this could be faked.
2) If the items appear for resale by the buyers later (how can you tell they're the same items?)... but this could be fake.
3) If PGP docs indicating I sold the items are made public, I would be unable to "resell" the same items, even if I had kept them... but you'll probably never see the PGP docs.
Realistically, neither of these three options is available to the layperson, so you're either gonna have to take my word for it or not.
And, finally, I hereby declare that I am flush out of Series-2 0.5 Silvers, so if you see me selling one down the road, I guarantee that I'm not the original owner.
Hope that clarifies things
