What does this have to do with an "open market price"? Most anything bought at retail price will not have the same resale value, that's just how resale markets work. They buy at wholesale and sell at retail. Pieces of jewelry and whatnot are not commodity bundles you can trade on a liquid market.
Retail art pieces aren't any different.. High dollar art trades at auctions (again, lots of liquidity), that's why they're easier to resell. But if you sink five grand into a piece from some gallery, good luck reselling it.