Just don't buy off of eBay.
There have been thousands of counterfeit SD cards mostly labelled as Sandisk. I bought one myself on eBay and was lucky to get a refund. But took me 2 months.
I ended up buying from a reputable store. In my case
www.newegg.com
Great price and service. But Costco, Radio Shack, Best Buy, Frye's etc are all good.