The Muggle angle is clearly the nerve to hit, here, and the clerk plays his part beautifully by giving Lucius a faintly unimpressed look at the notion of yes, Virginia, you call people here. People have phones and fancy little CiD devices and they don't lurk around all the time in shops that rely on Muggle technology that surely, surely a Death Eater would not work at, even a deeply anti-social one.

Surely.

"Sure thing, man." The clerk accepts the card, enthusiasm the very opposite of genuine - amusement, perhaps, at the ridiculousness of it all, but that's the extent - and his face stretches into a brief smile that is meant to humor Lucius.