Somebody--was it @boulderjohn ?--had an anecdote about a tank monkey doubting that a Trimix card sufficiently qualified him for a Nitrox fill.
This is why I have three cards in my wallet ... trimix, adv nitrox, and solo. With those three I should be covered. I never assume that my trimix card will allow me to get a 100% O2 fill. I've run into my share of clueless shop tank monkeys.