What's really going on in the shops this Black Friday?

Shoppers waiting in the US city of Columbia, South Carolina. Credit: PA Images

Retailers say it's called Black Friday not because it starts even before the sun comes up - but because this is the day no store will be in the red.

Like it or not this American import is now the start of the Xmas shopping bonanza. It's expected this year's will be the busiest yet.

What's really going on is a complex mix of marketing, merchandising and psychology. It is expected to generate sales of over £550 million - £360,000 a minute or £6,000 a second.

It all started in the US where retailers tried to capture customers on Thanksgiving break with special offers. but when those offers went online buyers anywhere in the world could see them - and Black Friday began to spread.

Read: 13 top tips on how to bag a bargain on Black Friday

Those in the know, like Tesco, say Black Friday will be busier than Boxing Day.

But firms with US parent companies like Asda, Amazon and Apple have more experience - UK stores have been used to pricing strategies centred on Boxing Day, something that could now count against them.

Be warned - this shopping frenzy can be used to camouflage old models of technology products.

Discounts can be over-hyped by comparing with the manufacturers' suggested prices, not the everyday price.

Plenty of things will be cheaper in the New Year clearance sales.

If you are headed out there - try to stay in the black!