Just remember that when you say "someone wants to buy a number of shares at a quoted price" what you really mean is "a giant investment bank or hedge fun

Just remember that when you say "someone wants to buy a number of shares at a quoted price" what you really mean is "a giant investment bank or hedge fund with some privileged information about a stock wants to buy so many shares that they actually need to go to multiple exchanges to satisfy their demand" and you'll be all set ;)