There is still a margin if the intended buyer was willing to pay more or would just want to buy the milk at whatever price offered. Of course, the grocers could keep raising the price arbitrarily but there is still a delta that the guy in the Ferrari could overcharge.
I think you understand the point we are trying to get across but just trolling it. I'd have appreciated an honest discussion rather than a trolling attitude.
The situation I'm describing is literally what happens in the real world. If a large trader wants to buy a big block of stock such that he can't fulfill the order on a single exchange he has to be pretty careful about how he executes the trade or the market will move against him. As soon as he purchases all the stock at the market price on a single exchange those selling stock on other exchanges will raise their prices.
It's very important to understand this. The price doesn't (generally) rise on other exchanges because someone swoops in and buys up all the supply. It rises because the people who were selling in the first place change their offers.
