The fine print
From the front of my Blockbuster receipt:
NOTICE: Starting Tuesday, August 05, 2008 the rental terms on the back of this receipt have changed. In select stores, including this store, rental product kept more than 5 days after the due date are converted to a sale. Sale may be reversed by returning the product o this store within 10 days of the sales data and paying a $1.25 restocking fee. This change supersedes any contradictory term on the back of this receipt. See store for details.
Of course, the back of the receipt is blank.