Are resell and resale used interchangeably or is that something else I need to learn?

Not to worry on this one! Technically, a sale would consist of an event where merchandise or service is sold in exchange for a reduced ticket price, while the sell of something or to sell something would simply mean goods or services in exchange for a designated price; both effort operations should include transparency and sincerity to earn customer satisfaction.  However, nowadays you can get away with either one, as the terms resell and resale are being used interchangeably.