It just shows even with the best will in the world issues on these models can be missed when selling and as in this case an issue that model had from the factory.
Ultimately for the benefit of both buyer and seller it's always best to fully check items before listing so that the buyer knows exactly what they're bidding on (mentioning any issues) and the seller doesn't have to sort out a refund. It shouldn't be blown out of proportion as many of us have had to return stuff to online shops etc over the years that we've been collecting.
I'm glad to see both parties have resolved this and we can all live and learn from it.