I think putting £100 when he wants £1500 is a good way to piss folks off!!!
And perhaps is also against the law :-
If you have advertised goods but have made a mistake with the price you are not obliged to sell you the goods at the lower price. However you should withdraw the goods from sale until the problem is rectified. Depending on the circumstances if you try to charge more for goods which are advertised at a lower price, then a misleading price indication could be given, which is a criminal offence