I would never buy on the Autoroute ANO, I agree totally with you.
I was 50km from home after a 500 mile drive, guage showing empty, computer showing 0 miles remaining, I am always good for another 80km at least but it was 5am on Sunday morning and I had been riding my luck for a very long time. It was only my intention to buy 5 litres so after such a long drive I was not worried about a couple of Euros extra.
Most of the autoroute fuel price displays were switched off as the price was going up so frequently, this one Total was on and it looked too cheap €1.949/l I pulled in to check and that was the price, 25cts cheaper than the supermarkets where I had been and I guessed 40+cts cheaper than the other Autoroute services so I put in 20l.
I passed another Aire station service and could see the price for diesel, it was €2.25 when I got home despite the hour I drove past Intermarché to check and they were at €2.25 as well! The next day I found that the GNR (red diesel) was at €2.20.
So on this occasion and probably this occasion only it was actually significantly cheaper at the Total truck stop service station on the Autoroute, there were hundreds of trucks parked up for the night so maybe they had discounted the fuel to get them in. I filled up at the car service station, the prices were the same at the poids lourd service station.