What are you really buying?
If you choose not to spend £25 on a pair of Marks and Spencer jeans, but instead opt to buy a pair from Louis Vuitton for £415, then you are buying more than just a pair of jeans. If all you wanted was a pair of jeans, then you could get those for £25.
What goes on in peoples' minds when they make decision like this is gold dust. If you can decipher it, you'll never struggle for prospects again.