We are not pet owners but we do like them. I always ask permission before approaching anyone's pet. I do this for my safety and to prevent an embarrassing moment for the pet owner.
If an owner is using a long leash or one of the extendable leashes I will avoid that person or ask them to shorten the leash to six feet or less. In private campgrounds the owners can set the rules but in most if not all locals, the 6 foots rules is written into law. I expect folks to keep their pets in their control and restricted enough that I can enjoy the area the just like them.