Demand for supply for private sale?

I'm a little irritated by this question and you can currently see the PS5 flying around at low prices on Ebay and "supply and demand" is often used as a reason. On Ebay or Ebay classifieds you are a private seller and therefore there would be no demand, at least no real demand, because the general demand is always there. However, you are a private buyer and thus you have no "customers" who have something on "demand". I can't find anything on the Internet about supply and demand in private sales. Now my question: is my "thesis" correct?

If there was no demand for the overpriced items on the market, there would be no buyers to pay the overpriced prices.

But there's, so there's also demand.

And besides, nobody is forced to buy and there's also no emergency exploitation, so there's no "usury" in the sense of the StGB.

Oh oh, interesting so it's about general demand, yes?

To meet general demand for a specific item, in this case the PS5.

What are you talking about? Supply and demand have absolutely nothing to do with private or commercial sales.

I discontinued my PS5 for 1 euro and it went away for 750 euro. Where does the price come from if not from demand?