Perhaps the statement was intended this way: "Shipping is 'free' [for Amazon Prime members]." That is a factual statement, even under a very strict definition

Perhaps the statement was intended this way: "Shipping is 'free' [for Amazon Prime members]." That is a factual statement, even under a very strict definition of the word "free". And I think it corresponds to the original poster's intent. Obviously, it costs money to become an Amazon Prime member, but for such members the shipping is, indeed, free.