that would be definitely a cool idea, will surely think about implementing, btw if you try a bit you can get the chocolate price to -2$ (negative 2 dollar) for a secret cutscene.
look behind the chocolate you will find that the chocolate is expired you can know that from the expiry date, and there's a clock on store which tells current date, each item has a hidden defect you need to find, which if you tell to the shopkeeper he will be willing to lower price even more
