I had no trouble refusing DCC this weekend in Barcelona, but I did pick up a couple amusing data points:

Paid at a bar with an American Visa via Google Pay, was offered DCC with a stated 2% markup that looked a little off. I did the math and the markup was 8%.

TMB (the main transit provider) fare vending machines worked fine with my CSR. Despite having a PIN pad with a display like most transit vending machines in Europe, the machine's main display offered to DCC me. At least the stated markup was accurate.

Question for people that spend more time in Spain than I do: are that many visitors really that naïve, or are there that many British visitors with 3-5% FTF for whom a 2% markup would be a good deal assuming it's accurate? (I leave Americans out since many American issuers would charge the FTF on any Spanish transaction, even in USD)