I believe he means that while there is an actual product or power supply that will be sent (as you said guaranteed by ebay), it could be fake in the sense that the product quality will be almost next to useless. It will probably stop working after a days or even hours, its power efficiency will not be at par, etc., etc..

I've tried ordering power supplies like these before and they are nothing better than generic PSUs you can find on sale at a junk shop. Stay away!