What an interesting thread, it sounds like Vienna is to pianists what Graceland is to Elvis fans!
clavierhaus I can see things from that viewpoint - the store owners don't want hordes of tourists dropping by and trying out the pianos, like kids trying out slides in a local park. They are running commercial businesses, not providing a public amenity. No doubt there are ways of discerning potential buyers/renters, and these people would probably get the red carpet treatment and may be given appointments out of hours to try out pianos.
"Don't let's ask for the moon, we have the stars." (Final line from Now,Voyager, 1942)