I asked Bob Garfield, advertising critic at Ad Age Magazine, about the whole before-and-after technique and told him I believed the ads.
"OK," Garfield said. "You're naive. … They're creating the illusion that you're going to achieve some miracle effect, when, in fact, you're not."
"Sometimes what the advertisers don't want you to know is that they're lying to you, which is what's going on here. They're lying with photographs."
Weight-loss ads aren't the only commercials that make promises that are too good to be true.
In 2003, "20/20" investigated the impressive before-and-after pictures from a baldness infomercial for Hair Genesis.
Dr. Dan Didocha, a disgruntled former business partner, told us that some had so much more hair in the after photo because they also had hair-transplant surgery, he said.
How could he be so sure? Didocha said he performed the surgeries himself.
He said, "In at least two of those [ad images], I know for sure that the main improvement was through the surgery."
It wasn't just on some of the before and after subjects, according to Didocha.
He said that he also operated on the Hair Genesis medical expert and the product's creator -- before their bitter falling out. The company insists the hair growth was due to its scientifically proven product.
What's more, Hair Genesis still uses the images on its Web site that Didocha's referring to.
So take Garfield's advice: Beware.
"Most of these before and after pictures work only on those who suspend common sense altogether."