Basic, sound advice, but on several occasions, legitimate, reputable bike shops have sold me or my loved one a bike that didn’t fit. By the time I figured it out, there was no going back to exchange it. These things can be tricky and while an LBS is the best place to go for most people, sometimes it’s not perfect.
Also, the type of advice I’ve seen doled out on this forum — ride as many bikes as possible, ask questions, figure out what you want to use the bike for (or the more specific advice about which models have disc brakes, etc.) — could be very useful and is not a “waste of time.”
Liz