Whether at PetSmart (or any pet store) or out for a walk in your neighborhood or visiting your vet, it is your responsibility as a pet owner to prevent any type of fight or other altercation from happening.
I show dogs, and regularly go to venues where dogs have to walk so close they might touch as we pass. People are courteous, keep a close hold on the leash near the head, & let others know when passing. There are intact males & bitches in heat... and surprisingly very few dog fights, or even tiffs.
If I am approached by someone who does not seem to have a good grasp on the situation (for example, while on a walk) I snug up the hold on my dog & say to them "please don't let your dog approach mine / sniff noses / etc. I'm not sure how he'll react" meaning my dog.
I DO know how mine will react, but what I DON'T know is how theirs will, or how they will handle any reaction from their dog. Many people have a very rosey view of their dog - they think that because their dog is good at home, & with the neighbors laborador, it gets along with all dogs, & everyone should sniff noses & butts & get along.
But, it doesn't always work that way, & the best way to avoid anything is to make sure it never happens, starting with your own dog.
T. - Breeder/Owner/Handler/Trainer Rhodesian Ridgebacks