In my experience - don't listen to what anyone tells you at a GNC or even small supplement store. I've met only a handful of guys (less than 10) that honestly had ANY idea what the hell they were selling - and I've been frequenting supp stores for about 9 years (since I was 17).
If I had known that along time ago - I'd have saved quite a bit of money....
And very, very few realized what a croc. their high prices were - relative to Nutraplanet, Custom, et al on the internet.