At the Apple Store I worked at, if someone brought back a defective product purchased from Apple during the return window, we accepted the product as a return, gave the customer a refund, and then (on the same transaction) sold the customer another brand-new one, right-off-the-shelf, accessories included.
If someone brought in a defective product that wasn't originally purchased from Apple, they were given the choice of either returning it to the store they bought it from (and getting another brand-new one, right-off-the-shelf), or they could have it repaired at the Genius Bar. Their choice.
Perhaps the receipt the customers sign upon receiving a Genius Bar warranty replacement, which states that the replacements may be refurbs, serves as adequate consent of the buyer. Because honestly, as litigious as people are against Apple, I haven't heard of anything in the US about Apple violating any acts by doing this.