was just about to post that hahaha
this is a general link, but it does have warning signs:
eBay Guides - FAKE SanDisk Ultra Secure Digital Cards Exposed
most of the time, they format it so it "appears" to have 16gb, but after a full format or copying of files, it will fill up fast, to like maybe 2-4gb. also, transfer rates will be
extremely slow.
Download H2testw 1.4 Free - Check your USB for errors with this tool. - Softpedia