A svelte woman appears on the television screen, grasping a weight-loss product that she says helped her shed 100 pounds.

Is she really a changed woman straight from the streets or just an actress reading a script — and does it matter?

"If an ad says this is an actual person, then it legally has to be," said Cathy MacFarlane, director of public affairs for the Federal Trade Commission. "Whatever [the person] is saying has to be true."

The method of using testimonials to sell products is remarkably effective, said Jack Feuer, media editor of AdWeek. "The best advertising is word-of-mouth. A classic example is the Hair Club for Men commercial: 'I'm not only the president, I'm also a member.'"

A recent promotional campaign for Apple computers features customers who switched from PCs to Macs, telling their tale of woe and then enlightenment: The PC always crashed, the Mac never does. The PC couldn't download photos quickly, but the Mac is a downloading dream.

"These are not actors — they're real people who have switched from PCs to Macs, telling their story in their own words," said Steve Jobs, Apple's CEO, in a press release announcing the launch of the campaign.

And according to experts, these kind of ads really work.

"[The ads] can be quite effective, especially in instances when you want to make a competitive claim beyond 'our stuff works,'" Feuer said. "They are saying 'your experience with us will be better than with someone else.' This is exactly what Apple is doing."

Oxford Medicare Advantage is currently running a campaign featuring senior citizens who demand better health coverage, as a voiceover assures viewers these aren't paid actors.

"In your own life as a consumer, a large part of how you formulate a brand preference comes from what other people have told you," Feuer said. "It is so powerful."

But getting real consumers to go from shopping mall to the small screen can involve extensive strategy.

In the mid-1990s, EPT pregnancy test commercials broke ground by featuring real couples in the moment they found out whether or not they were pregnant. The company used a phony market research tactic to uncover couples that might be expecting by passing out fliers and placing ads in papers.

"When people called in, they were asked a series of questions designed to identify couples in their 20s and 30s who hadn't yet tested for a possible pregnancy and were currently childless or had only one child," Sandy Horner, spokeswoman for EPT company Warner-Lambert, told the Chicago Tribune.

Twelve couples who were deemed potential TV material were asked questions about parenthood and whether or not they wanted a baby as the cameras rolled, which they were told was for a "research documentary."

With the tape running, the women were given the results of their pregnancy test. "At that point, they were asked whether they were willing to have their film used in a commercial," Horner told the Tribune.

But not every "real" person is genuine, according to one New York City actress.

"It's a given that at least some of the time the real people aren't real," said the commercial actress, who wished to remain anonymous. "I think you can tell by how smooth the person's speech and behavior is. They are actors … even when they're supposed to use real people."

"I think about some of the things I've said with full confidence, like, 'This is the best ever!'" she added. "I would be more concerned if this wasn't how I made my living."

The FTC does have testimonial guidelines, which they try to uphold, said MacFarlane, but in the end, not every "real" person is real.

"When in the course of investigations we find a product clearly fraudulently saying things that cannot be true we look into it, and if there are testimonials in it we look into those," MacFarlane said. "But we don't go out monitoring testimonials just for the sake of monitoring."

She added that in a recent study, the FTC found that 40 percent of weight-loss product claims were false.

"In the past 10 years the amount of false advertising in weight-loss products has skyrocketed," MacFarlane said. "And third-party endorsements are used frequently, which always adds credibility to a product."

While not every ad boasting testimonials will be true, experts say the straight-talking commercials are hard to beat.

"You don't need any foolishness, bells and whistles when you have someone standing in front of you saying 'Look, I'm just a person, I used it and I loved it,'" said Feuer. "You can't get realer than real people."