Most of my experience in motors for 30 years of being an electrician are for 3 phase jobs... if it spins backwards, swap any two of the 3 supply leads.

Single phase AC motors have a capacitor circuit that dampens the appropriate cycle at startup causing the motor to spin in the desired direction. Failure of this component is the likely culprit.

http://www.howeverythingworks.org/su...ric_motors.pdf

I don't suppose it's actually necessary to replace this capacitor, as long as the guy using it knows how to get it going in the right direction.... but there you are.