sold and supplied by Amazon directly is not normally a problem, even some retailers have been caught out with fake memory at times though, it's very hard to control I guess
we used to buy our memory in China and install in the cameras before shipping but it was getting harder to get genuine supply so we switched to ordering the memory direct from Transcend in Taiwan and delivering it to Australia and we install the cards ourselves, bit of a hassle but the best way to guarantee the integrity of the memory