I bought mine used but it was only 9 months old. I don't know what all this machine offers but you might be able to get some information from a Gammill dealer. It seems as if there's a way to see how much time is on it. Has it had any upgrades? They should be able to provide you with a great deal of information with the SN.
There really isn't that much that can go wrong that you can't take care of. Rick Taylor has a maintenance class (also available on DVD) that's extremely helpful.
If the seller is evasive or unwilling to provide helpful information, I'd probably pass on it though.