Upselling is a sales technique where the salesperson encourages a more expensive purchase by a customer by persuading them to get an upgraded version of an item or to purchase add-ons. Remember our food processor example? That food processor could probably be best used with a book of recipes, which also can be purchased at the same company’s website.
Affiliate networks offer you access to multiple (and by multiple, we mean hundreds if not thousands) of individual affiliate programs. They basically work by simplifying the signup process - instead of applying to become an affiliate for a each product you want to promote, you simply apply to join the network and instantly have access to hundreds of different affiliate offers.