I choose whichever deck I feel like using.
If the sitter is so insistent on a particular deck, they can go buy it themselves and learn to read. I used to be 110% focused on whatever the sitter wanted, and you know what? It's emotionally exhausting, and gets overwhelming trying to be a people-pleaser all the time. If you were a builder, you wouldn't let whoever you were working for decide which tools you got to use, would you? Of course not. You'd let them use what they knew best, what they were most comfortable with, what their professional expertise tells them is the right tool for the job.
I think of Tarot the same way. We're builders too in a way, it's just that what we build isn't palpable or tangible. So I pick the deck I want to use.