well there is a command /worth that tells you the value of an item. i personally like the fact that you dont have to go all the way to the store to sell something. It's much more convienent to just type a command to sell it. plus you can sell in different quantities and not just in a stack of 64; so if you have a stack of 64 and you want to keep half of it for tools then you can type /sell <item name> 32. or however much you want to sell. or just type /sell hand which sells all of that kind of item in your hand that is in your inventory.
Just something to think about you know.