Unexplained jargon in fiction

I picked up this Richard Stark novel in a local second-hand bookstore and was attracted by the reviewers’ descriptions of its main character (click the photo to enlarge). Funny how repulsive can have a contra-semantic effect. The ‘unforgettable Parker’, it turned out, is the same one played by Lee Marvin in John Boorman’s 1967 film Point Blank. Sold!

The Rare Coin Score has one stylistic detail I want to analyse here. Parker, Billy, Claire and Lempke are in a backyard planning a heist of rare coins. Parker, the ‘supreme bastard’ protagonist, has suggested a shortcut in packing the loot. Billy, a rare-coin specialist, explains why it wouldn’t work (note: he’s holding a spatula because he’s barbecuing burgers):

‘You take valuable coins,’ Billy said, gesturing with the spatula, ‘you just drop a lot of them in a canvas sack, carry them off someplace, dump them out on a table, you know what you’ve done?’

Parker said, ‘Tell me.’

‘You’ve lowered their value,’ Billy told him, ‘by maybe twenty-five per cent. Coins are more delicate than you might think. They rub together, knock together, the value goes right down. You go from unc to VF just like that.’

‘Billy,’ Claire said wearily, ‘they don’t know those terms.’

‘I’ve got the idea,’ Parker said. ‘The point is, we’ve got to pack them up, right?’