Re: They're doing it wrong.
I've never seen a festival system where the credit cards worked as quickly or robustly as cash. The first obstacle is frequently the connection itself. In a brick and mortar store this will be a fast wired connection that has probably been configured for months. Festival vendors usually wind up on wireless. Even if it isn't wireless, having just been set up there are likely to be connection issues. And that's before you get to potential power issues and training the temp staff to handle cards. In the US, you also get time for the signature.