Sometime the owners want unsold items returned and sometimes they want them to go to unsold lot listing. Most of the time the unsold lots price is about the min bid. I did buy one gun on an offer for less than that but have had several others declined.
Sold to unsold most of the times are items which the buyer failed to complete for one reason or another. Perhaps they failed to figure out how to import it. Perhaps their wife took the credit card.
I have had one item which I thought I had won at auction that later was informed it had gone to a higher bid. Never figured out that mixup but not being there in person does create risk for more confusion.
What I refuse to do is accept a sale for any item which I was bidding on and list. Seems like that would encourage shill bidding. I do watch for items that I lost to see if they come up again but so far only one gas and that was most likely just the new buyer selling it later.