I have to disagree with the OP not anticipating that her dog might react violently to strangers. The fact that she warned the man is proof that she knows what her pup is likely to do when touched by a stranger. And the fact that OP's pup did not go after people shows that either the pup knows better than to just attack unprovoked or that OP was in fact keeping the little guy close to her and keeping a good eye on it. But considering the guy felt the dog was nice enough to approach, I think we can safely assume that the dog wasn't just randomly yipping at people and showing signs of aggression. My dad's girlfriend owns a dog that was almost put down for his aggression (the grumpy old man, as we call him, barely has any teeth left. he literally can only gum you, lol) and by exposing him to people (who were specifically told not to pet him at this time), Stretch is no longer violent. So taking an antisocial dog out to a place like petsmart is a good idea. However, seeing as how there can be the occassional idiot who disreguards warnings like OP's, I do agree that getting the puppy used to a muzzle until he can be trained to stop biting might be a good idea for the puppy's safety. (wouldn't want someone to demand that he be put down. I've had plenty of friends whose dogs had to be put down cuz some idiot simply insisted on petting them despite warning given)

...You would sue if you went to pet SOMEONE ELSES dog, and they warned you not to, yet you took it upon yourself to do so anyway, and the dog nipped you? You are exactly what is wrong with the world right now. If you do something ******* stupid, it's your fault! Why can't people take responsibility for their own actions?! She warned the dog was untrusting, not that he might bite, suggesting that she did not know the dog would bite and felt it best just to warn the man not to risk it either way. Dogs that bite unprovoked are to be muzzled, ANY dog may bite under certain circumstances, and you can't just muzzle all dogs all the time, people have to use their own judgement and not go crying to the courts if they make an ass out of it.

Because petsmart is a store for pets that dogs are allowed... Not like she brought her dog to a grocery store...

I am aware that dogs are allowed in Petsmart. That doesn't mean you should bring a dog that bites into a public facility. Also, the obedience courses are basic and not for dogs with aggressive behavior.

Being a rescue dog who gets scared and needs to be approached carefully or else a nip of warning will be made isn't exactly an attack dog. If I told someone "please don't touch me" and they grabbed my ass, I'm not aggressive if I screech and slap them, I'm scared and defensive.

But you are a person and this is a dog. I have two rescue dogs. One nips. I don't take him into public.

Why muzzle a dog that is fine as long as it's not touched.. Seems pretty simple to me. Don't touch the dog and nothing will happen. If the guy left the puppy alone then the puppy never would have bit him, so why would muzzling the puppy be necessary?

Because you are clearly one of those people that don't actually read the original post and instead make up a situation in your head... The puppy did NOT nip because there were people and other dogs around, the puppy nipped because some strange man came up and touched him. I'm sure you'd freak out to if some stranger walked up to you and started to pat your head... So how about you think before you make some stupid assumption

The puppy socialization class is not for aggressive dogs.

It's not aggressive to be scared and nip without breaking the skin when approached without caution by a stranger after being a rescue pet. The puppy can't yell "stranger danger" all he has is fight or flight.

Any contact to a human by the mouth of a dog would deem the dog aggressive in the courts eyes. Some states even put the dogs down. Maybe a crowded public place is not the best environment for a newly rescued dog.