What is the practice of making the purchase of one product conditional upon the purchase of another?

The practice of making the purchase of one product conditional upon the purchase of another is known as tied selling. This occurs when a seller requires a buyer to purchase an additional product or service in order to obtain the primary product they initially want. This strategy can be used to promote additional items or services that the seller offers and can increase overall sales.

In contrast, cross-selling refers to the practice of selling complementary products that relate to the original purchase but are not mandatory for it. Bundling involves offering multiple products together as a package often at a reduced price but does not require the purchase of everything in the bundle to obtain any single item. Pre-requisite selling is not a commonly recognized term in sales strategies compared to tied selling, as it doesn't typically encapsulate the conditional nature of product buying.