hopefully you used Paypal or CC to buy and will have some level of
protection.
Read this info
http://reviews.ebay.com/FAKE-SanDisk-Extreme-Compact-Flash-Cards-Exposed_W0QQugidZ10000000001456539
If you think about it, Sandisk is a premium product sold thru
authorized dealers. There isn't any secondary market AFAIK. The
price right now for Extreme III 4G is US$120 (after rebate),
anything less is probably a scam.
I bought one of the fakes and had it returned for full refund
including shipping. If not for Paypal's intervention, I probably
wouldn't have gotten anything. The Seller I bought from also had
100% feedback and ALL of the people who bought them left positive
feedback until I notified them of the scam.
If it is a scam, DO NOT LEAVE NEGATIVE FEEDBACK, it will bite you
in the a$$. Simply contact as many other victims as you can and
hopefully they will leave negative comments. Once you leave a
negative comment you attract a negative comment. Even if it is a
scam, you will have a hard time getting it off your record.