I am uncertain who runs the M&S store at the service station near Benson in Oxfordshire but last night Ahmed upsold me two cans of Red Bull that I really didn’t want.

It was raining hard and I was quite tired when I pulled in to fill up the tank. 64 and a bit litres of diesel later I was delighted that the total on the pump was less than £100. As I looked at this I saw a sign that said buy two cans of promoted beverages and get 5p a litre off your fuel.

Inside the shop, after a comfort break, I bought a bag of crisps and stood behind another customer at the till. I noticed by the door a second piece of point of sale with the offer on it. After she completed her purchase, I handed the crisps to Ahmed, the teller, and put my credit card next to the payment terminal.

Are you interested in the soft drink offer, Ahmed asked, with a smile. I looked at him and as I did so his eyes flicked to the display of Red Bull behind me. As he was smiling I thought about it for a second and felt obliged to ask him how much the cans cost. He said something like £2.36. I shook my head, thinking that was a lot, and said I couldn’t work out if it was a good deal or not.

It’s a good deal for you as you’ve bought so much fuel, he fired straight back at me with another smile. Why not scan a couple of cans and then I’ll tell you what the price is, he said. And then you can make up your mind.

I turned to pick up two cans, apologising to the customer in the queue behind me. He scanned the cans and the price was over £100 and then fell below £100 as the deal kicked in.

OK, I said, pushing my card into the terminal. Are you planning to set up your own business, I asked him. That was a good upsell.He smiled.

Back in the car, as the windscreen wipers battled to contain the rain, I thought about the two cans of Red Bull rolling around on the passenger seat. I tried to do the maths and thought it cost me around £1.50. I didn’t want to drink either of them. But I still smiled and thought great customer service.