How do you know what memory brand does a card have before buying it?, neither amazon or newegg advertise it i think, thanks
You don't.
With sapphire they currently use samsung.
The best way to know which memory a manufacturer is using is by reading here and seeing what people are getting, they can and will change the memory type at times such as sapphire has done.
You can also look @ gpu reviews, often they take screenshots of GPU-Z especially in the overclocking part of the review, this way you can see the memory brand