I purchased a Kingston CF card on ebay and was contacted by our national trading standards and asked to answer a few questions, apparently these are the most traded fakes on the internet and yes mine was a fake so buy from a reputable dealer and you should be OK.
Sandisk cards are also infamous for being faked in vast numbers but luckily, I have never come across one. You do need to buy from someone you trust for all these things and that includes third party sellers on Amazon - be very careful.
Kingston Elite Pro CF card was quite slow for me and I thought it must have been a fake. I contacted them and they said it was a genuine one. So I concluded that was just how they were. They work ok but I wouldn't go out of my way to get another.