Well, I am starting now with bitcoin in Brazil (realizing my country is a non-concern in terms of the answer), I noted that final value change depends on exchange used.
So, if I buy a bitcoin in MERCADOBITCOIN (Exchange 1) for R$ 2383,00, I can sell this in FOXBIX (Exchange 2) for R$ 2500,00 in same minute. Is this difference in value normal ? Why does bitcoin have different values across different exchanges?
This is perfectly normal and a sign that the decentralized value system is working just fine. The valuation is different across exchanges because the value of Bitcoin on exactly one exchange is determined by the active trading on said exchange.
It just depends on supply/demand on each exchange. It is recommended to have a multi-exchange approach with an offline wallet holding the majority of your funds.
