There’s a cautionary tale on the Independent, warning about a new(ish) scam that can take place if you’re using your credit card abroad.
An Independent reader was checking their receipt after paying for a meal, and noticed they’d somehow agreed to pay in Sterling, rather than Euros. They hadn’t actually been given this choice, and they’d been charged a very unfavourable exchange rate in the process.
The conversion process is legitimate, but the customer should always be given the choice as to whether they want the bill presented in Sterling or the local currency.