With friends like that who needs enemies!!
Since you installed it, you know what the motor looks like and where it is located. using straight pins, push 1 into each wire. Then use a VOM meter to check for voltage, make sure the door is open, if you have a step that automatically retracts as we do on our 87 Southwind.
If you have power, look for a reset button on the motor, if there is one, it may have tripped to stop itself from burning up.
Either way, I would send the "friend" a bill for $465.00 plus your labor. Anyone who "borrows" something is responsible for fixing anything that gets broken. You may lose them as a friend, but then anyone who would lend out your mh without asking is not a friend you can afford to have around. Besides, if they had rented a mh, which they should have, they would be paying the dealer for any & all repairs.