"Quoted" prices
IIRC in UK Consumer law, the "contract" is made at the till, so the store can charge what it wants. However, it is also illegal to display an incorrect price on the goods or fixture, with a potential fine of up to £12,000 per unit incorrectly priced. If they overcharge compared to the fixture price, and you realise later, the law requires that if you return the item, they must give a full refund, but not refund the difference. However, which retailer is going to argue over a few pence or pounds, when the potential fine is enormous.
At least one UK retailer multiple tried to charge a punter more than the "advertised" price, so the punter did push local Trading Standards to prosecute them, and it was successful (substantial £000s fine).
I would love to know what the practical approach would be if the concept is extended to self-service fuel forecourts - pump says £1.30 per litre, fill up car, at the till they want to charge £1.50 per litre. Punter says ok then, get the fuel back yourselves.
More pertinent to the issue here is whether the practice on airline websites as described constitutes an "incorrect" display price, and if so, is the airline open to prosecution with a potential fine of £12,000 per unit. (Ie X seats currently available in the entire booking engine ) ?