The commission a bookmaker charges is in the odds; the commission a bank or a wallet charges is in the exchange rate. How to pick an account currency and how to stop paying three percent on every movement.
Most operators fix the currency at registration and never change it. Choose the currency of the bank account or wallet you will fund it from, not the currency the site suggests. A euro bettor with a dollar account pays a conversion on every deposit and every withdrawal, at a rate two to four percent worse than the market, which over a year costs more than the welcome bonus.
At the card issuer, when a card in one currency pays a site in another, at the issuer’s rate plus a foreign-transaction fee. At PayPal, at its own rate, which carries a spread above the market. At Skrill and Neteller, at their rate, with a stated percentage on top. At the operator, when it holds crypto balances in fiat, at a rate it sets. Each is a small percentage; several in sequence are not.
Some international platforms let you hold several currency balances; some wallets do too. They solve the problem for bettors who use operators in different regions, at the price of complexity. The simpler fix is one wallet balance per currency, funded by bank transfer in that currency.
Sites that hold balances in fiat convert coin to currency at deposit and back at withdrawal, at their own rate; ask what it is or use a site that holds coin balances. Stablecoins avoid the issue for dollar bettors and reduce it for everyone else.
Rarely; most operators fix it at registration. Open a new account only if the operator permits it, which most do not.
A bank transfer in the account’s own currency; failing that, a wallet balance held in that currency.
Conversion spreads, correspondent-bank fees on wires, or a withdrawal fee in the operator’s terms.