To fix some crowding in her teeth, Taylor Weakley, an environmental scientist in Denver, ordered teeth aligners two years ago from SmileDirectClub, a start-up she had seen advertised on social media.

At $1,850, the products were cheaper than braces, and she did not have to visit an orthodontist to get them.

But when the aligners did not correct Ms. Weakley’s teeth as promised, she asked for a refund. After a lengthy back-and-forth, SmileDirectClub said she would get her money back if she signed a nondisclosure provision as part of a general release form. In September, Ms. Weakley, 25, agreed.

“Going forward, I can’t say anything,” she wrote in an email.

What Ms. Weakley experienced was part of SmileDirectClub’s methods to limit information about customers’ dissatisfaction with its products. Seven people who ordered teeth aligners from the company described to The New York Times how the products did not fix their teeth; four said the aligners had created new problems that required traditional dentistry to correct.