Buying big amounts of Bitcoin for cash in person Presumably, I want to buy Bitcoin in person somewhere in Europe. I need very big amounts, say, 1K BTC, and I am willing to pay in cash (EUR). 

When I find potential sellers online or through friends, I ask them to prove they have access to these amounts of BTC by sending me 1 satoshi from their accounts or by giving me some other proof. However, they all say that they don't just want to show their BTC accounts as it's unsafe and ask for a video of my cash, which I don't want to provide first to anyone. 

How should I approach it? How are these trades usually done?
For large purchases, you should look at OTC (Over The Counter) Bitcoin markets. Also known as "dark pools".