I getting multiple errors with checkouts. Last night, the site would error out and then let the person pay again without letting them know the last one went through. I had three super angry people screaming that I charged them three plus times.
Also, if you click checkout and don't put in your credit card, it shows that you bought the item anyway. It also lets people download items with out paying for them through the same weird error.
Also, I have orders that get processed by Paypal that the cafe commerce backend doesn't pick up. It just doesn't show anything. I only know someone tried to buy something due to the paypal notification.