When I checked the price of Ether on CEX.io I noticed that there is a difference compared to Coinbase's price. Actually, the difference is more than 20$!
Does anyone know why there is a difference between these sites?
The price of cryptocurrencies (in general, not just Ether) is dependent on who's available who wants to sell them. There are several exchanges for different cryptocurrencies, and different individuals buy and sell on them, so one "whale" of a user (someone placing a large buy or sell order) can sway one exchange's rates by a bit.
Coinbase is a company that takes a profit from cryptocurrencies purchased there. There's a markup cost because you're paying for the convenience of purchasing Ether using your bank account, and without needing to learn to use an exchange/market to sell with another user (you're just buying directly from Coinbase). If you think that markup is too high, try another exchange and you'll likely find different rates there.
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