From time to time, customers will come in either with their Furr-Kids not leashed or they'll drop the leash, all the while assuring us that their Furr-Kid will "stay right by [my] side" or "he's really friendly." This changes the entire feel within the store as we now feel very much that we need to be on guard, take charge of containing the Furr-Kid and watch to be sure that no one else is coming in with their Furr-Kids, leashed or not.
People really do think they "know" their dogs. The problem lies in the fact that they know them under what, thus far, have been perfect or "normal" circumstances. But it isn't about the human's perception, it's about the dogs' perceptions. Any animal, 2-legged or 4-legged, will react accordingly if they feel threatened, scared, in danger, etc.. This isn't to say that there were actions intended to provoke those feelings. It's about perception. It can turn unintended actions and perceptions into something ugly and traumatic in an instant. The perceptions of humans are rarely the same as dogs and, more importantly, vice versa.
Worse yet, are the reactions of the humans when we tell them they must have their Furr-Kid under control while in the store. These reactions range from being obviously annoyed with us to eye-rolling to anger, rude commentary, disgust and even the promise not to be back. They don't realize that it's just not all about them. It's about the other Furr-Kids (and theirs) that deserve the right to be social without feeling threatened. A leashed dog is not on equal footing with an unleashed dog and they both know it.
Believe it when we tell you we would rather work directly with Furr-Kids than their people in many instances but until they pass a leash law for people, we will continue to focus on what is best for the Furr-Kids. Even while you're shopping, we're reading your dog's, and every other dog's, body language to hopefully preempt any negative interaction. We want every Furr-Kid to have a positive experience when they visit!
One more consideration...Leashes aside, allowing your Furr-Kid to run up to another is often a recipe for disaster. Imagine if some human you didn't know ran right at you and got in your face! Even if that charging human is grinning and seems excited, how would you react? It's intimidating, frightening, alarming, etc.. That's how dogs can react as well. In both humans and dogs, the recipients' reactions can be angry and physical.
Manners, social consideration and polite greetings/introductions benefit everyone and can offset misperceptions and negative reactions!