Most of the so called massive savings are far from what they seem. Almost all the sites seem to be claiming massive discounts on the recommended retail price NOT their normal selling price. Other items that seem like bargains are, as other contributors have noted, end of lines not wanted anymore so again not an honest bargain.
I have ordered a vacuum cleaner today as the motor burnt out on my old one, I compared a lot of sites and gave up on the black Friday "bargains" . I have also bought a few Christmas toys for the grandchildren but only things that I was going to buy, some of the cashback sites had extra offers ie higher percentage cashback for black Friday.
I find the whole thing really annoying as like many other things it has come over from America and doesn't have the same relevance here as it does there.
I would say I was on the non shopping side as I did not trawl through for any bargains and deleted all the emails telling what amazing bargains retailers had.