If a fake flash drive is a concern, use H2TestW as mentioned here.
http://fightflashfraud.wordpress.com/2008/11/24/h2testw-gold-standard-in-detecting-fake-capacity-flash/
If the drive's good, it should work with no errors. If it's burned with a fake capacity, it'll let you know what the real capacity was.
Also, if the drive is not fake but has a defect, it'll catch that too. I have had several Sandisk MicroSD cards go bad and H2TestW reminds me that the corruption problems aren't my fault, it's the card's... zowie!