I think maybe the idea behind the shops isn't what you think it is...
You buy an item for, say, 300 plat. (I've never even seen that much money all at once....
) Then you go and sell it, and receive 100 plat. Did you get gypped?
NO! Duh! Shops won't pay as much for an item as they charge for the same item. Identified or not, it doesn't matter. The shops have to make a profit, so they buy cheap and sell expensive. That's what makes the world go 'round. Walk into a shop, buy a bottle of water. You pay (at 9 Charm) 6 silver coin. Sell the water back. I think you get 1 silver. Basic economy.
Does WalMart pay the wholesaler $2.96 for that pair of fuzzy dice hanging on the rack? What do you think? Wholesaler probably gets $1.00 a pair. Shipper gets $.10 a pair. Associates get maybe a penny or two. And WalMart makes profit.