No, you're not a goose, or even a kangaroo.
When I visit an instrument shop, I carry a clip-on tuner and tune each instrument before trying. There's no way to properly evaluate an instrument if it's not at proper pitch. I'd carry a tuning fork, but often the shops are noisy enough to make tuning difficult. The clip-on is small enough to keep in my pocket.
Frankly, I don't care what the shop might think; it's my purchase. But honestly, I've never had anyone complain. Just the opposite, in fact. You're doing a service that the shop may not have time to do themselves, and they often appreciate it. And you're signaling to the sales people that you care about the instrument. If anything, you'll be taken more seriously.
I worked for some years as the main acoustic guitar salesman at a major shop in New York. And there was no way our duties allowed us to check and retune hundreds of instruments at the end of a busy day. But we did keep an A440 tuning bar on the counter for anyone who wanted to tune before trying. Nowadays, I've noticed that my local Guitar Center has a wall-sized chromatic tuner built into the wall for customers in the acoustic room.
On the flip side ... I recently bought a new uke from Buffalo Brothers here in San Diego. When I walked in, there were around 60 new ukuleles on the wall, from $50 to $3000 - and every single one was exactly in tune! This signaled to me that
they are serious. Impressive.
Now if we could just convince music shops to throw a fresh set of strings on their demo instruments every now and then. I can't count the number of times I've walked away from a display instrument because the strings are cr*p. Not such a problem for ukes, but steel string instruments ... Does anyone want to donate to the MTGuru string fund, so I can carry a crate of new strings when I visit the shops?