A family friend will help me troubleshoot my electronics. So, I have seen the other side of this: I get something which is completely nonfunctional and send it back to the manufacturer who claims it is functional, and tries to bill me for the shipping both ways. That's why if I can not get a working replacement in 2wk or so I just send it back for refund.
For a real example: Are you using very well made power supplies? Maybe your board's power filtering could be better, and customers notice because they buy the cheapest supply that meets their power requirements.