When setting prices, I would like to see not only the book value but also the sales prices other sellers have for that particular card.
You can do that if you click on the COMC "item number" under your card when you're in "Manage Inventory" mode. A thumbnail of your card will appear and you'll see everyone else's price. However, you won't see their actual cards. If it's a vintage card or otherwise condition sensitive, it's best to compare the condition with the other cards before determining a price.