> But the thing I'm stuck on is the places you can walk into and get cash for even one kilo of gold

My sister had been hoarding our mother's & grandmothers' jewelry for decades. I finally got her to sell off the gold before another of her bad choices in boyfriends stole the rest (last guy took her for about $40k). We took a check for it, but the guy had most of the $70k in cash at hand. No KYC at all. Here in the US.

Selling gold is still the Wild West.