I remember growing up me and other kids would always stand on a deck to scope it out at the skateshop, until we finally found "the right board" arbitrarily. I don't remember when I stopped specifically but I don't remember the last time I did it, probably 15+ years ago.
Do kids out there still do this at skateshops and why do we age out of this practice?
Surprised no one has said this yet, but "online shopping" has changed the way I buy boards and I note many others also rarely go into skate shops any more, compared to when that used to be the best place to hang out, talk shop, watch videos, etc.
Even the shops I do go into often don't have people who really know a whole lot about anything anymore, but there are not many shops I would consider a good core skate shop anywhere near where I live either.
As to standing on boards, absolutely the only way to do things.
I would always have a thick rubber mat near a board area, just for that purpose, as with the small place I help out with, I put down a couple of boards at a time for anyone to stand on to feel the difference in the concave, with some people being oblivious to differences, whereas others can definitely tell between a steep concave and a mellow board.