You'll very likely have heard the phrase 'abuse of the English language'?
Well, to me, using the phrase 'last chance to buy' is just such an abuse if not factually accurate. IW use it quite frequently, as do other channels no doubt, whether a strap line on screen or the presenter shouting 'LAST CHANCE, so check out your baskets NOW!'
Only it's not our last chance, is it. Okay maybe
sometimes it is e.g. if item is end of life or limited edition. However more often than not, in reality it's only our 'last chance' until the item next comes to air, which can sometimes be within days, usually weeks at most.
So I reckon the strap lines should read as follows:
Last chance to buy! (until a week tomorrow)