If the rate moves in my favor, I complete the trade and earn money (minus the £6 fee).

If the rate moves in the opposite direction I cancel the trade and retry in half an hour.

That's fairly standard, even among banks. I have a bank account and account with their FX desk, when I need to do conversions. They give me a spot rate real close to what you'd "seen on google", but I have to close the offer within the hour or it's not valid anymore. It's a big european bank.