I appreciate that the guy's attitude is just awful, but the author really should have given him a chance to respond/react before contacting his clients. Doing so doesn't preclude notifying them eventually. It's just common courtesy.
If I'm walking down a street and notice a broken door, do I have some obligation to track down the builder of the house and tell him about the issue?
To my mind, the good deed would be to inform the homeowner. At that point, I've done my part, and it's up to him to organise to fix his door if he wants to.
This dude went the extra mile even contacting the vendor.
I'm guessing the people on here all sympathise with the vendor because they can see themselves being in his shoes.