Actually, this is currently possible since when something has too high a value (such as the price of an item or the number of your credits) it becomes a (seemingly random) negative number.
Through godmodding I had several billion credits, and when I changed the value somehow (like selling or buying an item), it become a number like '-238592935900234'.
Anyway, I seem to remember it working the same way with item values, they eventually become negative so you have to pay them to take it away.
And here's a random fact... most junkyards in Scotland pay you something like £50 for your old car (cos they'll strip it for spare parts) - in England you have to pay them
