The neighbour in question is a house wife and 100% under the control of her hubby.
They have very clear divisions, this must be another one.
Thus one card per activity; in this case the weekly Tesco shopping trip.
I confess to only using my AmEx for petrol.
My business charges the % surcharge if you as a customer pays by c/c as we pay that same % fee to the merchant services provider. A d/c transaction costs me, the retailer about £0.30 + vat per transaction, regardless of the amount so as you'll appreciate, we don't pass that charge on top of any transactions.
Simply the terms & conditions of a small business, if you buy something from me for £3000, I end up about £85 out of pocket! Better to be out of pocket £0.30 I think you'll agree.