Bargain?

I think I've mentioned this before but here we go again :)
So I go into Tesco's last night to get a few essentials like bread, butter and coffee and as always I'm drawn to the "offers", luckily the brand of Coffee I drink is on a half price offer at £2.34 which is reasonable compared to other brands except the price last week was £4.28 so surely half price should be £2.14?
A large tub of stain remover the wife asked me to get was also on the half price offer at £6 but I had never seen the product priced above £8.50 in any previous visit?
The silliest one was a pack of Kellogs fruit and fibre clearly labelled half price with the £2 crossed out and for sale at .... £1.24? surely even primary school kids can work out 2 divided by 2.
So I got some bargains but still ended up feeling ripped off!!