buying fake ebay parts is pretty common. there are posts all over this forum that shows pictures of little tiny capacitors (among other things) inside huge ones, to give the appearance of a huge cap that the person was trying to buy. Stupid stuff like that.
It's one thing to buy parts off ebay that only operate on low voltage like 5 volts or something, but You are wanting to buy a part off eBay, hoping it WON'T be fake, and operating at 500-600v.
I can only ask one thing....are you Crazy!?
Spend the extra, buy a reputable part from a known supplier.
On another note, if you really MUST buy a part of ebay, look at the sellers 'other' items. If they are selling Bras, dvd, other misc stuff...then stay away. If the supplier sells nothing but electronics and surplus electronics, then your chances are better that you won't receive a fake. But, that only be a small improvement on the chance.