"I wouldn't do that"

the voice behind me said.
       "Well I just have," I said rather crossly.
Our greengrocer's shop is a lovely place. A lot of thought went into the layout. 
The produce is fresh and attractively presented. Where possible the owner sources local produce too.
They also sell a range of salads, fresh eggs (only free range), juices and so on. They also sell loose nuts and dried fruit. You help yourself to the required quantity with a scoop. 
While in the shop yesterday I noticed that someone had managed to spill eight or nine cranberries on the floor. Someone had trodden on one of them and I could see that there was a strong possibility of a sticky mess or, worse, someone slipping on them. It had only happened moments before and I doubted the staff, busy as the other end of the shop, had noticed yet.
So I waited until one of them had finished serving a customer and then I said, "S.... could I have a bit of paper towel please? Someone has dropped a few cranberries on the floor."
        "Oh, thanks Cat. You don't mind?"
        "Of course not."
And I didn't mind. I don't mind. It's the responsible thing to do. I know the staff well enough to ask for the paper towel and do that for them. If there had been a bigger spill or something which required more equipment I might have just left my trolley there, told them and then waited  until someone came to deal with it - which they would have very quickly. 
I know other people in our local shopping centre too. I  have occasionally "minded the shop" for more than one of them. Almost everyone works alone and they either have to get one of their colleagues to "watch" or ask someone else they trust.  They are not, under the centre rules, supposed to close their shops. Occasionally they do but they will be fined if the centre management finds out.
I don't mind. It doesn't happen often. I don't try and sell  anything.  I don't know how to use a cash register or a credit card machine or do any of the other things that need to be done.  I will help people find things in the bookshop - or suggest a picture book for a birthday present!
And I don't mind clearing up a small mess on the floor if it means that it might prevent an accident.
The other person  didn't see it like this. 
       "It's their responsibility - not yours."
I disagree.
When I handed back the paper towel into which I had folded the berries so that S.... could put it in their bin I was thanked with a cheerful smile. I knew I had done the right thing.