I am thinking about how are these all 'bitcoin shops' working. Imagine i go to a web page called http://bitcoinshop.smth where all i see is:
Price of the Bitcoin And all i can do is "Buy".
Of course the price of the BTC that they display is the lowest Ask price at the exchanges +X$ Fee they want to earn - makes sense.
Now the question is, what is happening behind the scenes?
I can imagine two situations:
a) They have BTCs in their wallet, so when i hit BUY - i get their BTCs out of their wallet at the price of the Exchange + their fee. But what if they bought them for 200$ and the price dropped to 100$ on the Exchanges? How do they manage that?
b) They are having market links to several exchanges and when i hit BUY they immediately place a BUY order on the exchange with the given price. Of course this is simplified as they should be looking into the order book and check the quantities and so on.. but nevertheless.
Still i see some issues: 1) They can't guarantee the order to be filled with the quantity i asked for, 2) They can't guarantee that at the time i hit BUY the price will be exactly as i wanted to buy. Well yes if the price goes down they get the money, but if the price goes up - well my BUY shouldn't be executed as i would have to pay more than i declared. This reminds me the old-days @ electronic exchanges - there was a regulation for this that the price has to be guaranteed for the buyer, but that's a different story.
Does anybody know how is that managed? And additional question, what if i come with a request to buy 10000 BTCs, i wonder how is that managed..
Example Shop: https://www.4coins.pl/en/