So I just tried shapeshift recently and thought it was pretty good. But from a technical standpoint, I was wondering how they actually perform the exchange of currency. Does anyone have a clue? My current assumption is that they're purchasing a target altcoin on demand when a request has been made (perhaps using something like bancor), then sending that altcoin to the recipient's designated address .
They have trading bots on various exchanges - like poloniex. On the other hand they have their own reserves of cryptocurrency. So whenever you trade there they see value and do trades with their bots. This is why if you trade with shapeshift you could be getting lower rates because they take some fee on top of providing you their service. However they are convenient way if you don't want to do verification processes or if you don't want to wait for deposit then trade and withdraw coins. It's fairly easy.