My rule of thumb price for a second hand item is about half current retail price at least for the initial offer and generally no more than two thirds as a final price. My reasoning is there is a high likely hood the item has wear and tear, you don't know the history of the item, (it may have been dropped ), some accessories may be missing, it's very often an older model, and there is usually no warranty, i.e there is more risk buying this way and the price needs to reflect this.
The selling prices tend to reflect my rule of thumb especially for the items I have been looking at. The expensively priced items don't sell even when they are relisted several times.
With one item I was interested in recently I used the "ask a question" to point out the asking price was slightly higher than current retail and made an offer accordingly. Also as I didn't want my comments to taint the auction for the seller I told the seller only to reply to the question if they wished to take up or negotiate on my offer, otherwise leave the question unanswered. They answered my question and turned down my offer. How dumb was that, now all bidders can see my comments, who will bid on that auction now.
Another person also "asked a question" pointing out that my comments re the asking price were very valid. They were told not all of these items sold for the price I had mentioned, in other words the seller was saying "I paid more for this therefore I can expect someone to also pay a high second hand price. I don't think they understand how the market actually works.
I know we all want to get as much as we can when we sell something, but you have to look at what the market is saying it's worth and price accordingly. I have seen at least one item not reach reserve because it was priced to high, it got relisted with a different reserve and eventually sold for less than the highest bid for the previously unsuccessful auction. The old adage often applies, "The first offer is very often the best offer"
What do other Geekzoners pay for second hand items?