I agree with Breezy, you might want be putting your pet at risk if you don't know if they're welcome at that house. I, personally, wouldn't bring them unless you know the person holding the garage sale and you know they don't mind. If you're just walking by and you don't know the people, it might be more polite to ask. If you see that their dog(s) is agitated, then it's best to leave and come back without your dog.
I grew up with the idea that dogs either belonged at home and walked around the neighborhood or only brought to places that are for dogs (like the dog park, the vet, pet store, dog beach, etc). This is as much for the dog's sake as the humans'.