Is it just for you for personal quilting? Is there a dealer nearby for support? Research what the service requirements are for that machine (i.e. yearly servicing at dealer?, what kind of oiling/maintenance does it require that you can do yourself?). Does the owner has service records for the machine? As long as it's been properly maintained, it will probably be fine, especially if you are just buying it for personal use.
But you really need to go and try the machine. See how it feels for you, since every machine feels different.