In essence, the unstated assumption is that if you bought it at $1 then it had a value of $1; and if you sell it at $2 then you added value, and we don't need to know how that value was added. Did you improve the item itself? Did you move the item where it was needed more? Did you offer it to customers who weren't served by others? Did you advertise&market the item to make it more attractive? These all are valid means of adding value.