Why do people make excuses for surly staff?

‘You grab that table, I’ll get the drinks.’ I did as bid. A couple of minutes later, Paul was back, beers in hand, and we started chatting. Soon the member of staff who’d served him appeared. She was stony-faced and holding a card machine. ‘You didn’t pay,’ she said.

Paul looked confused for a second, then glanced down at the machine.