But isn't it cash-only at even most established joints in Germany much less mom and pop immigrant-run hole-in-the-walls? My friend tells me even vape shops that sell hundreds of dollars of gear are cash only.

We have plenty of those in our ethnic neighborhoods. Heck even some very successful joints like Rosamunde Sausage Grill in the Mission District (S.F.) were cash-only until a couple of years ago, when I last went there.

Most other places accept cards & thus have to factor that into the price of the offerings.