I've recently been caught out twice, with a fake SD card and a fake USB drive.

Both were bought from China from different traders, both traders are power sellers with high positive feedback and few negatives.

Both products had been hacked. The 16GB USB drive was actually 2GB, the 8GB SD card was actually 4GB.

When I put the '16GB' USB drive in my PC it looked fine - under 'Properties' it read 16GB. I tried copying over a load of files, and they all copied OK. However after a certain point although it still looked as though stuff was copying across, all that was actually copying was a load of empty folders and files that would not open. So I started again, reformatting the drive, then copying a file at a time and opening it before copying the next file. And once it got to about 2GB then no additional files copied across successfully, even though it looked as though the files were there.

Same with the SD card - it read as though it was an 8GB card as stated, but beyond 4GB none of the files would open, I just got an error message.

Maybe I was just unlucky and these are reputable traders who are selling a few fake products unknowingly. However if they have sold other fake products it's possible that other buyers are leaving feedback before they realise, since the cards initially appear OK.

BEFORE LEAVING FEEDBACK TRY FILLING UP THE CARD / USB DRIVE TO OVER 50% OF CAPACITY, AND CHECK THAT THE LAST FILES TRANSFERRED WILL OPEN.

I found this out before I used the card and the USB drive so it's irritating, but not a disaster. However if you relied on this for important back-ups, or presumably if you put the card in your camera, you would lose your files.

I complained to the trader for the USB drive last week, who was apologetic, cannot understand how this happened etc, and says that they will refund my money if I return the item to China (I have just posted it to them, and I am confident that they will  refund my money). I complained to the other trader today about the SD card and received  a very similar response. In fact an identical response - it came from the same person and it gave me the same return address.