Firstly, you could check with the seller if the motor has every been changed and if they have receipt/invoice to prove it, that would be the ideal situation.
Secondly, check the speed and smoothness of the motor going up and down, it shouldn't appear to be sluggish or show signs of struggling. The roof takes about 15 seconds from the windows starting to drop in preparation for roof movement to them going back up and ending the process in either direction. The roof itself will release and go down or up in about 10 seconds.
