Daniel, the ballast should operate fine at either frequency. It's possible the ballast was designed to function best at 55 hertz thus making it both 50 and 60 hertz compatible for world wide use.
If the seller has an electric clothes dryer he may have installed a 240 volt-30 amp dryer plug on the power cord, plugged it into the dryer receptacle to test it and found it didn't work.
When it comes to ebay, the sceptic in me equates "untested" to be the same as saying it doesn't work.
In this case I hope I'm wrong and that somebody gets a good deal on their new search light. I looks like one heck of a cool toy.
Click on the blue and red ME icon beside power seller.
She says she has a twenty year old son. When I was twenty I would have been all over that search light in a heartbeat to see what I needed to do to power that bad boy up.
