I was beginning to despair of seeing another good subway ad worth blogging about but then I spotted one, for a popular online bedding retailer, with the statement: "Bedding so good it’s backed by a lifetime warranty." That’s no small claim.

So what are the rules for a lifetime warranty?

The FTC has Guides for Advertising of Warranties and Guarantees which are intended to "help advertisers avoid unfair or deceptive practices in the advertising of warranties or guarantees." The Guides are based upon Commission cases, and reflect changes in circumstances brought about by the Magnuson-Moss Warranty Act (15 U.S.C. 2301 et seq.) and the FTC Rules promulgated pursuant to the Act (16 CFR parts 701 and 702).

As the FTC helpfully reminds us, however, the Guides "do not purport to anticipate all possible unfair or deceptive acts or practices in the advertising of warranties or guarantees and the Guides should not be interpreted to limit the Commission’s authority to proceed against such acts or practices under section 5 of the Federal Trade Commission Act."

So what do the Guides say about advertising a lifetime warranty? Most importantly, the ad should disclose, "with such clarity and prominence as will be noticed and understood by prospective purchasers," the life to which the representation refers. When talking about products rather than people, the life at issue is not always so clear.

The Guides provide examples illustrating the potential ambiguity. A lifetime guarantee on a car battery could refer to (1) the life of the car in which the battery is installed, no matter if the car is transferred to someone else; (2) the life of the car while owned by the original purchaser; or (3) the life of the original purchaser. To avoid being potentially misleading, the ad would need clarification, such as, for example, for meaning (2) above, "Our battery is backed by our lifetime guarantee. Good for as long as you own the car!"

So, what’s a lifetime warranty for bedding? I’m thinking that must mean that if the sheets I buy rip under normal use, I can get them repaired, or replace them, for free, for as long as I live. That’s a big promise. In fact, it’s such a big promise, that LLBean famously withdrew its own lifetime guarantee last year. But the halo created by such a big promise may be worth it for this new company...at least for now.

Keep in mind that all kinds of warranties are covered by the Guides, not just lifetime ones. For example, the Guides provide that the terms "Satisfaction Guarantee," "Money Back Guarantee," or "Free Trial Offer," should be used only if the advertiser refunds the full purchase price of the advertised product at the purchaser’s request.