Tying is the practice of making the sale of one
good (the tying good) to the
de facto or
de jure customer conditional on the purchase of a second distinctive good (the tied good). A classic example of de facto tying is the selling of razors at a loss and making the profit on the blades. It is illegal when the products are not naturally related, e.g., requiring a bookstore to stock up on an unpopular title before allowing them to purchase a bestseller.
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