This problem is nearly impossibly for the average Joe to detect because the flash drive looks and works normally- until it's memory is filled.
Here's how to protect yourself from this scam:
Step 1: How to Buy
(if you've already bought an unbranded flash drive online, skip to the next step)
1) Buy a brand name flash drive
-Most brands are reliable in terms of storage. Most unbranded drives aren't
2) Know your product
-I was naive enough to think that many companies (including unbranded ones) are producing 16GB flash drives- I could be wrong, but I believe the only company selling one of that size is Corsair. This goes for any size...
3) Look on the packaging
-If the buyer shows a picture of the packaging, see whether the storage is printed directly onto the packaging, or if there's a sticker on it that has it. If it's printed on, it's more likely not to be a scam as that means the company probably hasn't tampered with it
4) AVOID BUYING FROM EBAY!
-Ebay has been seemingly overrun by scam artists selling falsely listed items- avoid buying anything that's not a well-known brand name from Ebay at all costs!
Step 2: When It Arrives...
1) Plug flash drive into computer and make sure it initializes normally
2) Download testdrive.exe and drag it into your C drive
3) Go to Start -> Run -> Type in 'cmd'
4) Note the drive letter that represents your flash drive and type 'c:\testdrive.exe (LETTER OF DRIVE HERE)' WITHOUT the brackets or quotes
5) Hit enter- the program will check how much space the drive thinks it has, and then attempt to fill that space.
If the program runs fine, congratulations! You have a normal working flash drive! However, if you get an error like the one in picture 2 below, the drive is falsely reporting it's space usage- return it and get a refund as soon as possible.
Step 3: Disputing With the Seller
If you bought it from another website, you may have a harder time getting a refund... I might recommend reporting the business to bbb.org (the Better Business Bureau) -they may be able to resolve the problems for you.
Thanks for reading- if you have any questions or comments, don't hesitate to post!