You can just buy pallets of returned stuff, you'll find a bunch of websites selling those via google, e.g. https://www.restposten.de/palettenware/retourware/ for a German marketplace. Most of the times you won't know exactly whats inside.

If you're interested in unpacking, without buying pallets of stuff, theres a small trend by YouTube influencers buying a pallet or two and looking whats inside.