Done right, a retail dressing room can be a real ego boost. The lighting is soft and lovely, the atmosphere can be relaxing (think Anthropologie), and the floor-length mirrors are flattering.

In fact, maybe they're a little too flattering. Suspicious shoppers have long wondered if retailers employ “skinny mirror” tricks to increase their sales. After all, how many times have you put a newly purchased piece of clothing on at home and been less than impressed? Making such a mirror wouldn’t be too difficult. As physics professor Dr. Ken Mellendorf explained to Apartment Therapy, all it takes is a slight curve in the glass.

"A completely flat mirror will show an image behind it of exactly the same shape and size as the actual object. Slight curvature along only one axis can make a person look fat or skinny. To make you look thin, your image needs to be compressed horizontally or extended vertically. Most mirrors bend over time top to bottom. If seen from the side, there is a slight curvature in the edge. The top and bottom edges are usually straight. Your home mirror can do this due to its own weight. If the center bulges out a little bit, your height will appear slightly smaller but your width will not be changed."

Yes, even non-retail store mirrors can be deceiving. Thin mirrors are more likely to bend and distort over time, while thicker mirrors—especially those supported by a frame or mounted on a wall—will present a more accurate image.

But back to the dressing room: Though the existence of “skinny mirrors” has been pure speculation in the past, there’s now evidence that such sorcery is real. In 2015, entrepreneur Belinda Jasmine appeared on Shark Tank to pitch The Skinny Mirror, a line of mirrors designed to make reflections appear to be up to 10 pounds lighter than the person really is. None of the Sharks bit on the deal, but Jasmine continued with the business and has apparently been in talks with at least one popular apparel chain. There’s certainly good reason for that anonymous chain to investigate: According to The Skinny Mirror website, stores that use the modified mirrors experience up to 18.2 percent more sales per customer.

Though many customers see the mirrors as consumer deception, The Skinny Mirror website argues that the product helps create positive self image and better self esteem, leading users to feel more confident and satisfied with themselves.

When it comes down to it, are skinny mirrors helpful or harmful? We’ll leave you to reflect on that.