So as in title, Is it possible to buy really large BTC amounts? like a million $? What was the largest amount of BTC you bought at once?
It is a big yes! but that will depending on us of how can we but a large amount of bitcoin. Probably if you are kind of elite people that would be easy but if not it will take a due time process before we get it.
most of the time when we are selling bitcoin we do not know the seller we just depend on exchange and therefore you need to select a trusted exchange because you have no concern with the person that who is buying your bitcoin you are just selling it in open market.