Don't misunderstand me, I am not in any way defending the dealer. If it happened the way you say it did, and I assume it did, they were negligent.
I will just say that this is a perfect example of why purchasing something like this - sight unseen - on the Internet is a bad idea.
Even if both parties are being sincere, there is the posswibility of a different concept of what 'mechanically sound' means. Not saying that happened here but it's always a possibility in the best of circumstances.
But to buy something 'as is' that you have never seen is a recipe for disaster.
Good luck to you, if it's running now, enjoy it and good luck. I wish you well.