In PFSOP, it is possible to gain free objects. Their resale value is zero, so I added a wand of cure light wounds to my character by customizing it and giving it a cost of 0.
Changing the number of charges in the item made the item value go into negative; I was expecting it would not change, because it would be relative to the cost of the item bought; not of the normal cost of the item.
This might be a new feature but an object whose value is negative means you need to give money to sell it.
Custom cost now has a minimum of 0.