Then they charge $30 to reject the transaction, another $30 when you go "odd and try to swipe again", then extra money because you didn't have the $30 to cover

Then they charge $30 to reject the transaction, another $30 when you go "odd and try to swipe again", then extra money because you didn't have the $30 to cover the fee in your account, then recursively until you're $1200 in the hole and they're refusing to cover it.