In general, selling processes are profit-oriented. A seller's, especially a shopkeeper's, main aim is to make profit.
Nobody wants to sell an item to lose money.
But there are some exceptions. The seller may need some amount of money urgently. In this case, he sells an item without considering profit. In another case, the seller knows or strongly guesses that if he does not sell a particular kind of item with a little loss, he will not be able to sell it in the future at all. Therefore, he can accept to lose some money.