Companies like Space NK, Harrods and Sephora have all sold out of their main calendars already.

The Harrods beauty calendar was priced at £250 but claimed to include items worth £1,600, while Sephora’s £199 calendar said it included items worth £1,000.

But you can find people selling them on eBay, asking up to £550 for one from Harrods and £399 for one from Sephora.

“It comes down to supply and demand – dynamic pricing,” says Sarah Johnson.

It may make sense to buy it even at an inflated price, she says, if the retailer is out of stock and you can’t get it anywhere else, especially if you perceive it to save you money. on the total value of all items. .

This, however, raises the question of why companies don’t just earn more.

Ms Johnson points out that this is a seasonal product and they don’t want to order too much and end up with excess stock that they would then have to reduce.

Space NK told the BBC it had produced 30% more stock this year than last, but due to “unprecedented” demand, stocks were still sold out within two and a half weeks . He plans to increase production next year.

Despite the expensive nature of beauty calendars, Ms Johnson says there is a “perception of value” there.

“People might buy it to take it out and give it (individual items) as gifts. There’s an element where people treat themselves and are also very savvy and save money in the long run.”

With more and more Advent calendars on sale today, it was thought a few years ago that we might have reached the “peak” of the Advent calendar.

But Cissy disagrees – and thinks it’s the opposite.

“They always sell out every year, so I feel like there’s room for more.”