You should always ask before you approach. Sometimes dogs don't like other dogs, then if the owner knows this they tense up and make things worse. Some people don't want strange dogs by there dogs just because, but its there option. There is also the fear factor, as your dog gets older you will see people go the other way to avoid you and there is nothing you can do about it.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD