Fighting back against supermarkets

The adverts are everywhere, "Shop at Asda, when you get home, goto the asda website, enter your receipt number and we'll compare prices against the other supermarkets via [insert a price comparison website here] and if it's cheaper elsewhere, we'll give you the difference...." blah blah blah

This advertising campaign and so called offer, runs alongside asda prices, increasing all over their store.... why?

It's well known that "knowledge is power" - tesco's club card is very successful at obtaining shopper's data, which leads to more profits as they can then use this customer shopping habit knowledge, to charge higher prices on products that are good sellers in particular areas of the UK.

This is what I think Asda are doing with their latest campaign.
Only this time, it involves a price comparison website, who also get to see the data!
Why else would the prices at asda be shooting upwards?

Which ever supermarket you shop at, I suggest doing your own style "price checker" - keep your receipts over the course of a month.
Each visit highlight the regular products you buy each visit, every week.
Then compare the prices and how much they fluctuate.... it'll be an eye opener for you!