It's quite simple honestly, if you profit off something, you have the responsibility to make sure it's legal. We all like platforms like YouTube where you can find anything you want, but the truth is that they're currently unsustainable when forced to comply with the law.
With the advent of AI there's hope for improved systems for detecting violations, but it doesn't seem to be there yet.
If you re-sell for example stolen goods, your proceeds from those sale may be taken from you together with whatever stolen good you have on stock, and if you are found to be aware of the illegal origin of those goods, then you are an accomplice and are charged accordingly.
That's why buyers of used items have the difficult task of ascertaining whether those items are stolen or not.