For advertisers, it's a sneaky trick to get you to buy their products. For consumers, it's called deception.

The two key words savvy shoppers need to watch for are: up to. Advertisers use them to deceive consumers into believing that products perform better than they actually do on average, according to a new study from the Federal Trade Commission published on Friday.

The study looked at how consumers responded to window advertisements that claimed new windows would lower electricity bills. The FTC found that a significant portion of consumers believed they would save the maximum promised results on their energy bills when the promotional copy included the phrase "up to."

In reality, consumers typically save far less than the maximum savings that are advertised. The FTC's study found that when an advertisement said customers could "save up to 47 percent," nearly half of consumers believed that they would actually save 47 percent. In reality, the average savings was 25 percent.

"Advertisers using these claims should be able to substantiate that consumers are likely to achieve the maximum results promised under normal circumstances," an FTC press release stated.

While the copy trick is not new for advertisers, the FTC has been cracking down on window companies and others who greenwash their products, or make environmental claims--like energy and cost savings--that are not as supercharged as they appear.

As global environmental issues have received more attention over the last decade, advertisers have jumped on the bandwagon to trumpet claims about energy savings or other pro-environment benefits. While some claims are true and there are more eco-friendly products on the market than ever, green marketing lifted the sales of products with a bare minimum of sustainable eco-attributes--at least temporarily.

Windows, and other household items with energy-saving claims, have been the subject of the FTC's recent investigation. Earlier this year, the regulator settled charges with five window companies who made unsupported efficiency claims. The federal agency publishes guidelines for how companies can use product certifications, seals of approval and other eco-friendly claims.

For consumers, buying new windowsis a major capital investment. More efficient panes can cost between $7,000 and $20,000 depending on the size of the house, according to Consumer Reports. Homeowners can expect to save between 10 and 25 percent on their energy bills by replacing old windows with new ones, the consumer magazine reported.

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