Should you buy acai berry in a retail store like GNC? Of course - but it's easier to order it online. Although the acai berry is rapidly growing on popularity (especially after it was featured on Oprah) and it is making it's way to more stores all the time, it's not really easy to find at normal stores yet. Ordering it online is way easier ...and you can also get a free trial of it.
For only like $4.95 shipping and handling, you can get a free sample here:
http://www.mb01.com/lnk.asp?o=1873&c=28405&a=22938
I Strongly recommend this option before doing anything else. GNC acai berry is the same as you'll order online, but it's far more convenient (and cheaper) to order it online via the above link. Good luck!
