Twice in recent weeks I have given a masseuse more cash than she asked for, in payment for the extra service ( once intentionally she was brilliant and I felt a bit flush anyway, once by accident, in the dim lighting I though a £20 was a £10).
Both times the girl has said I'd given too much and gave me back the extra.
Never happened to me before, I'd always thought that they'd just keep it, so a welcome change to usual transactions.