Right Now: (BTC to USD Price)
CoinBase: $2577
Preev: $2566
CoinDesk: $
2634Poloniex: $2528
Bittrex: $
2520Its like that, different sites have their 'own' market, if one person decided to buy all the bitcoins and bring the price up to $3000 on one site, it is possible. You can be a medium of all these sites and make small profits, but bare in mind the fees too.