I had it years ago with office cleaning contracts, I did a load of extra work for this 1 company and I cleaned their offices everyday for years. When my wife was in labour I still went in as she is never quick a births. I let them know this and I still lost the contract because another company was slightly cheaper.
The thing that bugs me is that this other company cleaned offices in the same building and I decided not to even try to put a quote in on theirs because I would feel bad about that (their living & all) what a mistake that was.
Anyhow I had made them sign a 3 month dismissal contract and held them to it. Durring this time I stuck to my cleaning spec, no extras, no nothing. They kept leaving notes around telling me to do this and that, but no way. They called me in as I was not doing the extras. When I told them I had always done it as extras they were shocked because it really was a lot more work, and I had been doing it for over 3 years. They showed me the spec of the new cleaners and I found that they would be doing even less.
Tough luck on them.
Anyway getting back to the point, I agree with chepstow. When that office clean went it really hit me for quite some time.
I have a lot of good work but I try never to rely on it although most the time I do.
The problem with supermarkets is that they are know for this sort of thing. There really isnt any loyalty there.
Still if they wanted them cleaned and it was a good earner then I would do it.
Steveyboy