Generally I have the right money with me, and like some I carry a bit extra should I want to extend the meeting. However I have been given change back by a WG once - cash machines generally give out 10s and 20s, and I stayed 45 mins with a WG once, and at the end asked her how much - she said call it £45 but of course I hadn't got any fivers. So I said "here's £50" and she surprised me by saying "hang on, let me check my purse" - pulled her purse out, rooted through it, and gave me back £5 in £1 and £2 coins. I thought fair enough, thanked her, and left.