.. i will return and solve everything 
Sometimes card with VirtualPub is cloned by some script instead display of proper ads. Or sometimes blank page is displayed. When two VP in two browser cards are displayed every click is counted as two. For example I was click ONCE 25 beers and script buy 50.
I had the same problem.
maybe you are clicking twice accidentally, because when i what to buy several sigarrets or whisky, i and doing like this and its works.
be perusal and good luck