Gabriel Carrera, along with many others like him, bought Bayer's One-A-Day WeightSmart diet supplement. Apparently, he didn't lose the weight he wanted, because he filed a class action alleging that Bayer had fraudulently claimed that the supplement's use of epigallocetechin gallate (a green tea extract) boosted metabolism and assisted weight loss.

It turns out, however, that Mr. Carrera hadn't kept any receipts, and, in deposition testimony, confused WeightSmart with various other products that were not part of the litigation. (Relying on class members' recollections in defining membership is notoriously tricky.) Nonetheless, he argued that either retailer records or affidavits from class members would suffice to establish membership.

Relying on these arguments, a court for the District of New Jersey certified a class in Carrera v. Bayer Corp., ruling that despite the fact that the plaintiff had conceded that identifying anyone who bought WeightSmart (which disappeared from shelves in 2007) "will not be easy," any management problems were only "speculative." It was particularly reassured by an affidavit from a claims administrator that the plaintiff submitted.

On appeal, the Third Circuit disagreed. Pointing to its ruling in Marcus v. BMW of North America, the Third Circuit held that,

Depending on the facts of a case, retailer records may be a perfectly acceptable method of proving class membership. But there is no evidence that a single purchaser of WeightSmart could be identified using records of customer membership cards or records of online sales.

Moreover, it was not impressed by the claims administrator's declaration:

The [Administrator's] Declaration does not show the affidavits will be reliable. Nor does it propose a model for screening claims that is specific to this case. And even if [the Administrator] produced a model that is specific to this case, we doubt whether it could satisfy the ascertainability requirement.

The takeaway from this case is a simple one: ascertainability matters. If the defendant does not have records of the class members, and the class members cannot be trusted to remember their purchases, a class action may not be the appropriate vehicle to try their consumer-fraud claims, no matter how small they are individually.