>"That's a mistake" sounds right but if the market is willing to pay, then was it really a mistake?

But it's not willing to pay. That's my point. That's why those postings sit unsold.

>If the average price were a good deal, it would by definition not be a good deal.

Let me clarify: I mean "good deal" in comparison to just buying new. Take headphones, which is something I've bought used a few times. I found a pair of SHP9500s for like 20% of the price of new ones; they had some visible wear, but they weren't broken and they sounded perfect. That's what I'd call an excellent deal. Another time I found a pair of HE400ses for 60-70% of the price of new, and they looked mint. That's a good deal and how the used market should work. The buyer pays a little less with the risk that the item might have some latent defect that's building up, and the seller gets to recoup some of his money.

A bad deal is paying 90% for that same risk and uncertainty, which is what I see most often. Yeah, maybe the product is even verifiably in good condition, but at that point the difference is so small that why would someone even bother?