Good question. I suppose they might have a sample pack of Zeiss lenses for those who normally wear glasses. Maybe not perfect, but maybe good enough for demo purposes.
WRT contacts, according to what @xdev wrote, it’s primarily an issue with hard lenses and (I think) the majority of contact lens wearers wear soft lenses. But even with hard lenses, the device will work, but it may not track your eyes as well as it should.
But, IMO, this is a good thing. If it won’t track your eyes well in the store, then that’s a clear sign that you shouldn’t bring one home, because it won’t work any better there.