Depends, did the person bidding 1000 dollars bid after the ended auction in which I agreed to sell it to the highest bidder, which happened to be $500?
How do we know that there was another offer? How do we know that you simply didn't like the price that the auction ended at? I could hold an "auction" and then if it didn't go as high as I wanted, just say that I had another offer. Then I have no downside. I get the advantage of a bidding war without the potential consequence of the bid not going as high as I'd like. Win/win, eh? Except for the people who bid in the auctions in good faith, that is. And that's why you now have negative trust.
At this point, I'd like to point out that these appear to be the exact same type and quantity of PSUs that you "sold" to someone else after you backed out of your auction. Coincidence? Or maybe you just happened to have 3 more laying around, right? That must be what it is. Surely you didn't do exactly what I said above and backed out of your auction because the price didn't go high enough for your liking, and now you're trying to trade the same goods for something else? Nah, surely that can't be it.
Left you some trust myself.