Just like on eBay where you can look up completed listings, there should be a place in the CS where you can look up an item and see the last 10 that were sold and for how much they went for, and perhaps the date they sold.

I've been trying for a while now to buy some of the more rare items, and it seems that everyone really has no idea what they are worth, and then when someone lists one for sale in the CS, now everything thinks that is the correct price even though that may be way overpriced. Then when it disappears from the CS, we don't know if it actually sold for that much or if the person just removed it. There should be a way to see actual sale prices for items. That will help buyers and sellers get a feel for what items are really worth.