If is online, over the phone, etc., you can return or cancel for any reason within 7 days. And this also include services. For example, if I sign up with a new ISP, I can cancel it within that 7-day period (even if it have a 1 year contract).

If it's in-person you bought something, technically you can only return up to 30 days for non durable goods, and 90 days for durable goods, if there's some problems with the product, or a reason etc.