The thing that jumps out at me is you all TOWED the vehicle to Midas. For whatever reason, if I tow something because I don't want the engine running, I'd never let a Midas guy start the engine unless I was there....then I'd do the starting. That should have been made clear to them, IMO. If it was, even tacitly, then the Midas folks are holding the bag for starting a new or untested engine without permission. You didn't say whether it was new or not but if it was, who knows if it was even primed before the muffler wizard fired it up to "hear the pipes" he installed.