Rav Yitzchok Grossman , Rosh Kollel of Greater Washington and Dayan at the Bais HaVaad…
Question: If someone has an Amazon business and realizes on Pesach that some products that he’s selling contain chametz, is he permitted to keep the profits?
Answer: First of all, it is clear that it is forbidden to sell chametz on Pesach. It is forbidden to derive benefit from chametz on Pesach, and selling them for profit would definitely fall under this category; therefore, if someone accidentally sold chametz on Pesach, he should not take the profits.
If he made a shtar before Pesach that stated that he is selling all his chametz to a non-Jew – both the chametz he knows about and the chametz he is unaware of – the status of the proceeds will be subject to a machlokes haposkim. In a famous teshuva, Rav Moshe Feinstein writes that if a store sold its chametz and then continued to do business with it over Pesach, even though the store did the wrong thing, the sale is still valid. Many Poskim, including Rav Elyashiv, disagree and say that by doing business with the chametz on Pesach, the storeowner displays that he is backing out of the sale and therefore it becomes null and void.
If someone sold merchandise on Amazon, it is very hard to stop the sale and it might not be so simple to just not take the money. One should have in mind not to be koneh the money and should find a way of discarding it without benefiting from it.
Similarly, if one owns a vending machine that will be used on Pesach, even if he sells the chametz in it he still would not be allowed to take the earnings, as this would constitute benefitting from chametz that was sold on Pesach. Instead, he should have in mind not be koneh the money and he should somehow discard it.