He does have to turn a profit on what he's buying. You want spot price? Oddly enough, in California and maybe other states, a pawn shop will give you spot price.
But of course there will be a large bid / ask spread on collectibles and small quantities of precious metals. Dealers have to make a profit. Anyone who doesn't like the price is free to sell on eBay or at a local coin show or something.
PS: eBay charges 14% or something. I also know very well that Pawn Stars is scripted, but the business side is true to life.