Fair use of testimonials in advertising is too important to take for granted. Other creative tactics and techniques change with the fashions of the day, but the testimonial is such a workhorse selling tool that it never goes out of style. So when a top federal ad regulator expresses concern about possible misuse, marketers should sit up and take notice.

J. Howard Beales III, the new director of the Federal Trade Commission consumer protection bureau, said in this newspaper last week that some current testimonial ads raise questions about "whether the [advertised] product is responsible for the advertised benefit." That's a very basic issue, and one that certainly could open the door to FTC investigations of particular advertisers, and eventually even lead to prosecutions.

Testimonials have been the focus of previous FTC actions. The use in ads of actors in "white coats," which suggested they were physicians, triggered one notable crackdown. An endorsement by a celebrity with an undisclosed business interest in the product triggered another.

This continued concern by regulators reflects the continued credibility consumers are willing to give to testimonials. That acceptance gives testimonials a power that marketers should protect. When the product experience for most consumers doesn't live up to testimonial-fed expectations, all testimonials can suffer. And that means marketers should welcome periodic government scrutiny if that's what it takes to maintain consumer confidence in what endorsers have to say.

Established law, embraced in the ad industry's own self-regulation programs, requires marketers to back up material claims with evidence, or a "reasonable basis." Making a claim in the form of a testimonial does not free a marketer of the responsibility for having that "reasonable basis." Nor does hedging, by saying the endorser's experience is "not typical," ease the likelihood that some consumers might be misled.