Until recently, I did not realize that Amazon.com has entered the second-hand goods market more directly. They, of course, have always welcomed vendors who, in effect, want to run their own small second-hand shops via Amazon.com web site (much like Ebay vendors do). But now Amazon.com actually invites customers to sell goods directly to them: when you browse the web site and look at a product page, you often see an offer to buy this particular product from you - the line of business which, in which, in the US at least, has been mostly reserved to pawnshops so far.
How good a deal do you get, compared to the retail price of a particular product (new or used)? Not always very good. For example, the web site offers to sell you a Nokia N900 cell phone / pocket computer for $160-190, and they can buy it back from you for $3.25. (That's three dollars and twenty-five cents). And, by the way, the payment is not in cash but in the form of an Amazon gift card.