Maybe more of a WWYD. Our cleaner has been with us for around four years. She's lovely, and we have a good relationship, but if I'm honest, she's not very thorough and will use excuses like "oh the door was closed so I didn't think you wanted me to do that room . . . " 
I pay her £12 per hour (plus agency fees by monthly direct debit to her agency).
Our normal arrangement is 3 hours a week, which is £36. I don't usually have £36 exactly so end up leaving £40 most weeks - which is fine, it's not her fault if I don't have the correct change, so I accept that she takes the full £40.
A couple of weeks ago, I asked her if she would be able to do a full-day "deep clean" - inside cupboards, skirting boards etc; eight hours at her normal rate of £12 per hour. She said yes, and that she'd like to do a weekend and split it over Saturday and Sunday (four hours each day). Perfect, great, thank you.
DH and I went away for the weekend so I left £100 (8 x £12 = £96) but noticed on the security camera that our cleaner only spent six hours at the house on the Saturday (which would be £72) but when we got home, we saw that she took the entire £100 even though there are several things that could have been done to take the time up to the full 8 hours we agreed.
It just rankles a bit. She already leaves 20-30 minutes early on a normal week (we never get the full three hours) so this is a scaled-up version of that; I feel that if she only worked six hours, she should have taken cash for six hours and left the rest.
However my gut feeling is just to leave it and say nothing, in the grand scheme of things it's not that important . . . what do you all think?