Both Superfit and Fun-Fit have printed a toll-free number on their exercise products to provide round-the-clock telephone assistance to any customer who encounters difficulties. Since customers only call the numbers when they find the exercise equipment difficult to use, and the Superfit line receives three times as many calls as the Express line, Superfit’s product must be more difficult to use than Fun-fit’s.
Which of the following, if true, most strengthens the argument above?