Interesting thread. This happens occasionally with any brand. Then once a customer gets truly dissatisfied, I am not sure there is any way to recover. Let's say they get the tractor working perfectly, then 2 weeks from now he is mowing and a twig mysteriously reaches up and pulls a wire loose up under the side panel. Then it doesn't start. I assure you the first thought in anyones mind would be to blame the tractor. Then two weeks later he accidentally gets some fouled fuel, "stupid tractor". So a little thing becomes a big thing due to the history of the machine. So the writing on the wall, so to speak, is that the machine needs to go away, regardless if they can fix it to perfection or not. The faith in the machine is gone, so why own it?
I don't see this thread so much as a NH quality issue, although there have certainly been a number of real issues, but I think more can be learned regarding how a dealer handles a customer when everything starts falling apart and a customer loses faith.