No signs of life in 2nd hand servo

[colmo]

I bought a KO Propo 2113 FET servo from another Oople member, and just got around to fitting it in a car.

Alas, the servo showed no signs of life when I powered up the car or tried the steering wheel.

I was careful not to plug it in with reverse polarity.

What is the most likely explanation (apart from 'It's dead, Jim')? Is there anything I could do to test it?