I'm currently travelling in the UAE with various UK issued and therefore GBP denominated cards. DCC has been offered at most places - hotels, shops, restaurants, but it has been clear on the terminal - press 1 for x£ or press 2 for yAED. Good.

Where no choice has been presented, my suspicions are heightened, but it has so far always been charged as AED. I use a curve card with a 1% fx fee and it messages you instantly on a charge being made with the charged currency and amount and actual GBP cost, so you can see what's going on.

Also I had to book a QR airline ticket from DXB to DOH. The ticket is priced in AED as the point of sale is Dubai. The website defaults to offering a £ cost, but is clear you can 'press here' to accept charges in AED.