Dang, that's too bad for you. I bought my Kioti used, private party, and when the check engine light came on, I asked my local dealer as politely as I could if they would troubleshoot if for me and possibly repair under warranty. They were extremely friendly about it, and transferred my warranty over for a small fee. As a result, I gladly paid them full price for an implement I'd been wanting. If they had denied me warranty service, zero chance I would have ever, EVER set foot on their property again or given them a single dollar.
When you get paid directly by a manufacturer to cover repairs under warranty, why do you care if the customer originally bought the tractor from you or not? It actually makes no difference to you financially at that point, and you lose the prospect of any future business with that individual (or 3 or 10 more depending on how word spreads). Just seems like stubborn pride, you know? It's not like someone goes to a different dealer to intentionally screw you out of a sale, and then expects to walk all over you for warranty coverage in the future.