Comment by DamnInteresting

They did try adding variations to the amount (+0.50-1.00) late in the game, but by then it was ineffective, I could still quickly detect them and turn on the randomized data poisoning. I expect that they want to keep the amount small so most cardholders won't bother to look into the unfamiliar charge.

I do wonder whether these people sold their list of "verified" credit card numbers to any criminal enterprises before they realized the data was poisoned. That would be potentially awkward for them.