Well, I picked up the generator yesterday. Got it home and popped the cover off. Things are worse, but better than I had hoped. I don't know why, but for some reason they were trying to take the cylinder head off. The fuel line to the injector was disconnected and they had cut the return fuel line. There was also a 18" length of 3/8" fuel line laying inside the enclosure, but I don't what it would have come from. The mechanic had also taken the exhaust manifold flange bolts off, took the valve cover off and took two of the cylinder head nuts off. Sadly, the monkey they had working on the unit didn't try to take the two bolts supporting the muffler off and instead tried to pry the muffler off the studs. I'm pretty sure he bent the muffler flange in the process. He also tried to pry the intake manifold off, but only removed one of the mounting bolts. Ended bending the flange to the point the intake cracked. I can see rub marks where he had tried to pry the cylinder head off, but it wasn't coming because the muffler hadn't been removed. I don't know who was working on the engine, but he was a total idiot. We're talking about Jeremy Clarkson level of mechanical skills.
When I pulled the cord the engine felt very smooth, but clearly wasn't building compression. I removed the muffler (which requires the starter to be removed) and pulled the cylinder head off. Piston looks perfect and the cross hatch is very bright and clean. Honestly, I can't see anything wrong in the cylinder. There was a small piece of exhaust manifold gasket stuck in the exhaust valve, so I'm hoping that was enough to keep the engine from building compression.
At the moment I don't see any reason why the engine wouldn't have run. Of course, I don't have any of the parts the doufus had removed. I'll try Green Mountain generator this morning to see what used parts they'll sell me and then talk to my local dealer for the remaining parts. I've ordered Yanmar parts in the past for my compactor and they're not terribly expensive. All told, I'll probably have less than $100 in missing parts.
Sadly, from the other photos, I have a hunch that all of these gen sets were sold because they didn't work. The best case scenario would be for you to get a unit where they got into the engine like mine and then gave up after a half hearted attempt to fix it. If there was something wrong with the electrical side of things, I don't know if it could be fixed.