I get it. I don't like it, but I get it.
Look for a Ryzen 7 laptop with 16GB RAM from Newegg. I mean specifically check 'Newegg' as the only seller. You get two choices starting at $900.
Then uncheck 'Newegg' as the seller and sort by lowest price. You get 24 of the exact same laptop from 24 different sellers with an $80 spread in price. And that's just the cheapest 24 items. There are hundreds more. They start from $650.
For every $900 laptop Newegg sells from its own inventory, they have have to source it, receive it, photograph it, inventory it, ship it, etc. For every $700 laptop from somebody else, they have to...well, do almost nothing. Somebody they don't employ does all the rest. They just keep their web app up and running. Granted, the development of the site is expensive. But it's not expensive per item.
So they can make $50 off every $700 laptop with a minimal expense of pennies per sale. Or they can make $50 off some $900 laptops that cost them pennies + $150 labor per sale.