Look for the lack of serial number on the usb portion that you stick into the drive.
Then test it with h2testw.
Even before that you can try loading it up with a video lets say and then attempt to view it.
Corruption exists with none to minimal playback.
You could also put other files on it and try to read them.
Start h2testw with an 8meg test and then validate it.
Odds are it fails.
All h2testw does is write a series of files and try to read them back to see that they wrote properly - corruption means a failure and corruption is due to a fake capacity drive.
Don`t buy off ebay or other site.
Buy this drive only in a reputable big name store.
Otherwise you lose your money,
time and get great frustration.
Another thing to notice is the speed of writing...
check the specs..
The fake drives are really slow.