The seller is 'inviting offers to buy', under the law nothing is offered for sale. The contract is not complete until the seller accepts your offer to buy. Any retailer seller can demand the correct price in a mistake or misunderstanding. Trading standards can take action if there is ' intention to deceive', but in a civil court you could only claim damages against your losses, which would be nil. Buying online confuses the issue slightly as to when they accept your order. Nowadays if you read the Tems & Conditions it will say the contract is not complete until your order is dispatched even if they have taken payment.