Interested to know what they meant by "bad" fuel? Did it contain ethanol? Was there water in the fuel?
I presume the fuel would have been "fresh" fuel, not some that had been setting for a period of time where it had time to go bad?
If the fuel was bad from the start, I don't know of any product that could turn it back into "good" fuel, but Star Tron is claimed to be one of the better products to slow the breakdown of fuels containing ethanol. Marine-grade Sta-bil is another.
Sucks especially when you have a brand new sled to have this happen, hope the dealer is right in the diagnosis of the cause of the burn down.