As someone who has been sold a fake memory card i can sympathise with everyone who has suffered.
However many cards will work just fine UNTIL they reach their capacity then all the content is lost and the card is inaccessible.This happened to me on a trip around Australia,back at a friends house in Melbourne we tried all sorts of recovery tools and the PC would not even recognise that a card was in a slot.
On my return to the UK ,the "seller" from where I had bought the card around two years ago had gone,so no luck there.Along with some friends we decided on a simple test of filling various cards to capacity to see what happened,obviously after all photos and data had been saved.We just created folders of mp3 files and photos just OVER various sizes of memory cards and then copied them on until they reached capacity.
We discovered four fake cards all of "2 gb" capacity amongst our collection, all the fake cards were bought off ebay and had worked well for some considerable time but had never been anywhere near their full capacity,everyone also said that whilst cheaper than at high street shops they were not that cheap! which may have given us all a reassurance that we were getting what we paid for!
I now go abroad with a large selection of old 128,256,one 512 and one1gb cards all in all @ 4gb!! ,lots of cards to carry but if you lose one or corrupt one your holiday is not all lost.
It was interesting that all our fake cards were 2gb and mine was a 4gb,mostly because I had decided I did not want to carry around lots of little ones and my friends had not yet got round to upgrading and buying bigger cards.Looking on Amazon there seems to be a lot of negative comments of 4gb and above,sizes seem to have moved on.
We have all come to the conclusion that small is beautiful ,and you can look a gift horse in the mouth.