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. ‘Oh, it didn’t go through?’ The staff member shook her head. Paul held out his card, she punched the numbers again, we all waited for the beep. Then she handed him his receipt and left. ‘Service with a smile,’ I said. He laughed. And then, a second or two