I was referring to this case. Out of interest, what regulator and regulations are there for allowing the exchange of fiat currencies?
From the FinCEN guidance:
Dealers in Foreign Exchange
A person must exchange the currency of two or more countries to be considered a dealer in foreign exchange.19 Virtual currency does not meet the criteria to be considered "currency" under the BSA, because it is not legal tender. Therefore, a person who accepts real currency in exchange for virtual currency, or vice versa, is not a dealer in foreign exchange under FinCEN's regulations.
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http://fincen.gov/statutes_regs/guidance/html/FIN-2013-G001.htmlSo from that is seems reasonable that one could, from the U.S., accept EUR in exchange for BTC (and vice-versa) and not be considered a dealer in foreign exchange. There might still be the requirement to register as an MSB, but not as a "dealer of foreign exchange". Now if you try to go USD --> BTC, then those BTC --> EUR, then that effectively is a USD --> EUR trade and those transactions might cause you to be considered a dealer in foreign exchange.
As far as what regulators exists for a forex brokerage? Here's a snippet from a forex brokerage:
In American the main Forex regulatory commissions are the National Futures Association (NFA), Securities and Exchange Commission (SEC), and the Commodities and Futures Trading Commission (CFTC). These bodies regulate Forex brokers in the US and ensure that only registered brokers are able to operate in the country, and that transparency in all transactions are maintained.
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http://www.etoro.com/education/american-forex-regulation.aspx