I believe you are speaking of UK here, as am I. In theory there are minimum periods for which a product must be offered at the advertised 'full price' before the retailer may offer a so-called discount.

This is the reason you will sometimes see a little tag on an advert giving details of some obscure branch of the store in the arse-end of nowhere which has, for the minimum time, offered (but failed) to sell the item at some grossly inflated price. This enables the chain to offer a pretty bogus bargain.

You may recall an old comedian's routine of a chap who is asked how he can be so certain of a date in the past, he replies "Oh, that was the day I went to Allied Carpets, but they weren't having a sale, I put it in my diary."

One good thing about the internet is that it has made quick comparisons between different retailers much easier, though it is no help when looking at 'own brand' goods, such as most furnishings. For such goods you can only go by whether you feel the price offered is a good deal or a bad one. Regular store visits over a period before purchase can help, but they can also be pretty soul-destroying as well.

On the whole I try to ignore the hype, like MrH I find most of the offers largely meaningless.