Can you describe what you do when trying to purchase something at the Pawn-O-Matic? I think pressing Enter would result in a "sold". Can you buy other stuff there?

Try this: select the Item you want to buy and push the "Use Item" Button. This should work.

You probably have the same problem i did, i was using a finnish keyboard with a portuguese layout and i couldnt make any selection in the pawn-o-matic, including the exit. I set the layout to the original hw language and went to the controls setup again. Now, even if you see the correct key listed, rebind it. You should be able to use it normally after.