Haven't run into it just on fridges, but have on all kinds of other appliances. As I don't fix appliances, I usually stop there.
Other than a basic light circuit in the refer, the only other electrical componants are the thermostat, and the compressor. The light or thermostat wiring could short to the frame... But the most likely culprit would be the compressor. Most household refer compressors are hermetically sealed in an dieltric oil case. The oil can become contaminated if the refer is leaking, or an indirect short inside the compressor could give you some strange voltages, as it is going through the motor to the case. Anyway, not a good item to not be grounded. That ground is nessesary to clear the fault (Short or indirect short) by tripping the breaker or fuse. Thats what the EGC is for, ensuring that exposed metal parts are the same voltage. It used to be that ovens and ranges had the neutral and ground bonded. Then if there were a neutral problem elsewhere you could get neutral to ground current. Which is more painfull than a simple shock IMO. But sounds like your customer got "locked on". I have been once, and it was one of the most frieghtening experiances in my life.
