Thanks for the advise. They are asking $300 and I will need a single phase motor. I am kind of leary since I can't hear it run. I just really want to find something other than the super loud Husky I have now.
If you could hear it run to verify that the compressor had no knocks and pumped up in the proper amount of time, I'd pay that all day long. Or if not running, but it had a single-phase motor on it, same deal as it would be worth that if either the pump or motor was good.
But not running . . . do you feel lucky? It's not a horrible price (just see what that pump sells for alone, yikes, about $1500, assuming it's a Champion R15). And you can get repair parts readily, but they aren't inexpensive. So really up to you. It's an order of magnitude above your Husky compressor in terms of quality, but that also comes with a cost.
Worst-case, you buy it for $300 (or maybe offer them $200-250), buy a 5HP motor & starter for $400, and then have to put another $300 of parts into it plus your time. $1K total for a compressor that you can get new for around $2K. This of course assuming that the tank is good (bad tank = dealbreaker). Best-case, you get it for $250, and get a good deal on a used 5HP motor+starter, and you have a working compressor for around $500.
If you're on the fence, keep the contact phone number and call them back after a month or two to see if it's still available. I do this a lot. I figure if it's gone by then, it wasn't meant to be.