Well, I'd like them to clip it's wings so that people can hold it. They're more likely to buy it if they've held it. But regardless, you can't tell anything about a GCC in the store. They take awhile to settle in (say a few weeks in your home) before their true assertive nature kicks in. Think of them as tiny macaws & you'll be right on track. Really.
(I have a macaw & she's actually less assertive than my eldest GCC!) They *will* try to rule the roost!
But they're small, so you can just pick them up & put them where you want them. They figure this out.

And *unlike* the macaw, their bite is no big deal, if you've got well seasoned dish pan hands, especially.

So that all makes it easy to keep them reasonably in line. (And it means the penalty for letting them get a bit spoiled & willful isn't as great as it is if you let the macaw get out of hand.)
I've got 3 GCCs. They should never be kept singly, IMO. They DO nip. It's just in their nature. They're plucky little boogers. They pretty much have to be because they're so small. I would never catagorically recommend them for kids for that reason. But then, if your child works well with the bird (and if the bird decides it likes her) she may win it's heart, in which case it will be very good to her. Which is not to say that it won't occassionally still nip her. (Thankfully their beaks are small.) They are possessive of their person, though so be warned! (That's another huge benefit of keeping a pair. They get less possessive of a human family member.) But again, this relationship would take time (months) to develop & isn't something you could accurately test out in the store. Unlike bigger birds, I just don't think GCCs are as easy to "feel out" just by a few store visits.
You *can* reliably tell how friendly & hand tame they are by how they are at the pet store - and this one clearly is very tame, and very touchable. More so than most, I'd say. By far. (I'd say this would be a great bird!)I would say that this particular GCC is already way more "touchy feely" than most. If you like the bird & can afford it, I'd say buy it. You'd be doing it a favor, and you'd be able to work it into your home, if not as a "finger/shoulder" bird, then for certain as a "watch & laugh" bird. They're great fun to watch!
If it is too nippy for your tastes, get it a friend. In fact, I'd say get it a friend anyway. They are just incredibly social - mine don't even groom themselves - they take turns grooming each other! They are also just the very cutest birds to watch of any that I have, because of all that social interaction. And they're **very low maintenance** when kept in pairs. Fairly quiet too, and cheap to feed, cheap to buy toys for (because they're so small). I have a trio, actually - all girls. And yet, mine have stayed totally hand tame, step up etc with no problem at all. It's not true IME that you will lose their "pet potential" if you keep them in *same sex* pairs or groups. (Now, if there was true mated pair bonding going on, I don't know what would happen.)
It will do just fine with your dog. In fact, it's more the *dog* I'd worry about!

My cats regard the GCCs as holy terrors - with good cause!

The cats literally run for cover when the GCCs swoop down upon them!