As there is are always two sides of a story, I'll spill out mine too.
I am not going to copy all the emails sent between on a public forum, but if a moderator wants the copies, I'll be more than happy to send them the copy.
The buyer contacted me about a problem with the unit. I've replied within an hour to the email. Asking specific questions about the installation procedure.
He said that it was installed by the dealer. I contacted the dealer, and from what I gather then installation was done wrong.
I still offered the buyer, to ship the unit back, so we can further inspect the unit. If the unit is defective, I'd be more than happy to refund the unit plus the shipping paid to send it back to us.
But if it wasn't defective, we'd simply send the unit back.
The units have 2 year warranty, and we stand fully behind it. We all know dealership mechanics as well, no need to comment further on that.