Not necessarily - if the website is only authorising transactions then transaction isn't contractual until vendor 'accepts' the order on processing and 'captures' transaction. Technically an authorisation is not a sale so this way sale of goods act isn't breached. NB this is how all amazon transactions are processed - marking for dispatch actually 'captures' transaction. I have no idea how argos operates though and wouldn't be the first one that might actually be breaching sale of goods contract if it's just charging cards prior to dispatch/processing. Also in cases where it's been brought to anything close to resembling a judge they have sided with the vendor saying that price discrepancy is obvioiusly wrong in cases where a large 50 inch TV was sold for a pound or some such.