Stark sounds like a great puppy, congrats! Like the others have said, it's just a matter of desensitizing him to all the excitement of the pet store. I was lucky with my puppy, because most of the pet stores in my area give out treats, so when he was younger and very food motivated, he always wanted to go up to the counter first. Now that he's older, he's not interested in the treats anymore. But he's used to being in the stores, so he's calm. The various treats at eye-level get his attention, lol.
I know it's hard to have 2 different people with 2 different ideas of what to expect from a puppy. But since he's your dog (like mine is) you get to call the shots. Since Stark is doing so well with everything else, you're obviously going about things the right way.