These are a waste of money and just don’t work.
There are a lot of scams around - type in “acai berry scams” to the search for questions and read answers.
All you need to lose weight is a good healthy diet and exercise 
February 20, 2010
Any Good Results From Using Acai Berry Or Colon Cleanse To Lose Weight?
February 8, 2010
Are The Acai Berry Tablet Found In Local Stored As Good As The Ones Advertised Online?
The acai berry craze is filled with SCAMS, especially on the internet. I definitely suggest trying to buy the product in a health food or vitamin store. Probably your best bet is Sambazon or another product with a well-known brand name. I suggest using the powder instead of juices, which are probably filled with water and sweeteners.
In terms of scams, I am speaking from personal experience. I ordered a free trial of acai berry Power 500. On my next credit card, I noticed an extra charge of $29.95 from that acai company. I called them and they said I had agreed to a personal nutrition consultation for $29.95. To make a long story short, I had to threaten them with a lawsuit before they refunded that extra charge.
I also ordered acai berry Supreme. A few weeks later, I got another bottle in the mail, even though I never asked for it. I left the shipping box unopened and wrote on it: Return to Sender. Do Not Charge My Credit Card for This Product. Then I put the item back in a mailbox. I am worried about what my next credit card will say. I’ve heard of people being charged $89 for the next shipment.