If its an 09 make sure everything is updated that can be.  Check the cab suspension to see if it works, if the cab settles a lot, clicking the button 5 times will reset it, it will top out then bottom out or maybe its the other way, cant remember. Light modules do go bad a lot also but no way around it really. The hydraulic couplers also go bad a lot, it may have the latest and greatest update on it, not sure how they turned out but all of the latest and greatest before it weren't any better. 

As mentioned the A/C is poor and loud. If its much of an issue tint the windows.

They have their quirks, but if you can buy them right they aren't the worst tractor to run depending on what you are used to and many think they are comfortable. They are smoother than some others.  The Fendt CVT/Rear is great as is the Sisu motor. Very efficient, quiet and smooth. Just the agco stuff around it that can be a pain.