You mean that the machine operators could be doing a double spend? In every case they take the dollars before they give the coins, so you have to take the leap

You mean that the machine operators could be doing a double spend? In every case they take the dollars before they give the coins, so you have to take the leap of faith... I don't find that scenario sensible at all. First buy $1000 machine, first customer comes in, buys bitcoins with $50, and notices that the machine does double spend. I believe he is not going to tell any of his friends...