Is it forbidden to use products made from pigskin, and what should be done with products that were purchased unknowingly, and is the seller who did not inform the buyer that they were made of pigskin sinful?

It is permissible to utilize pigskin if it has been treated and tanned, according to the preponderant opinion. Therefore, there is no harm in acquiring a bag made from it. However, abstaining from it is more virtuous, due to the Prophet's (peace be upon him) saying: "Leave that which makes you doubt for that which does not make you doubt."