I agree that some take the piss. But surely if you see a offers of 50% or greater there is a reason for that. When making a purchase if you don't take the time to look around and compare like for like then I don't see how you can complain.
I alway see this as "sales and marketing" if you not clever enough to work it out that's your problem. Most of the offers are for non essential items so if you feel you need them that's your choice.