Coinstar machine undercounted, no disclosure of minimum amount needed to avoid fee Internet

I was cheated at a Coinstar machine in Alamo, CA today.

I noticed that my coins were being undercounted, so I stopped the transaction. Instead of getting the Amazon gift certificate I had requested, I was informed that I did not meet a minimum amount necessary to obtain the certificate and that I would be issued a cash ticket minus 10%. So I lost twice - once by having my coins undercounted and twice for the cash ticket fee. Nowhere on the website or machine does it indicate there's a minimum amount necessary for a e-certificate - or at least it's not obvious - I looked carefully for such a minimum. There is also no way to cancel a transaction.

I filed a complaint with my state attorney general and the Better Business Bureau. I feel that

1 - AG's should audit the accuracy of Coinstar's equipment.

2 - Coinstar's equipment should allow cancelation of a transaction

3 - the minimum amount needed to avoid a fee should be prominently posted on the website and machine

I will never use Coinstar again and I will tell everyone I know to avoid them like the plague.