Regarding eBay, you need to set up an account (free to set up) in order to check "completed listings" when you search. Completed listings does show what items actually sold for, but it's subtle. If the list price is *green*, it means the item sold for that price. If the price is green but crossed out, it sold for some unknown best offer price. If the list price is *black*, it means the item was listed for that price but did not actually sell. You can click on individual completed items to get a little more information about the original listing if you need it.
To search for completed item prices, make sure you are logged into eBay, do your search, and then scroll down on the left side until you see "Show Only" and click the box next to "completed items".