If the model is high rebates at some times (e.g. an article costs €50 instead of €100 for part of the time), then you do save money buying when it's at €50.

But you have to remember that €50 is the price at which the seller would usually sell the product. That's the price that their price calculation says that it should be sold at. Otherwise they'd not be making profit.

So the alternative model is to always sell the article at €50.

Or to put it differently: The seller does the price calculation and comes up with €50 being the price where they would need to sell it to make profit and the price that the customers would still buy it at. It's the optimal price, and the price they should be going with.

Instead, they sell it for €100, so they can discount it to €50 and put a big "-50%" sticker onto it. Hardly anyone who has the choice buys at €100, everyone waits for the sale, when it's put to €50. And then more people buy, because they think they have made a massive deal, because they have gotten a €100 item for only €50. They are going to tell all their friends about it, it might even make it into news articles or stuff like that, and then more people buy.

The other option, which is illegal in some countries but legal in others, is to just fake the "full" price all together. The product is always offered at €50, but the sticker says "€100 -50% super sale!"

You can see stuff like that on Aliexpress. Pick some article that has a 50% rebate during some sales holiday (e.g. Black Friday). Then look at the article a week later, and in almost all cases the non-rebated price next week will be the same as the rebated price during Black Friday.

People just love being lied to. It's really sad.