I think the first question is...does the owner see a problem with the way the dog is behaving? Are there people left at home that have to put up with the dog's anxiety? If there's a recognized issue to work off of, then it might be a lot easier to get onto the topic of training. Personally, I tend to tell people flat-out when their dogs need training or when they're unknowingly provoking undesirable behavior, but I've also been training dogs for years so most aren't offended by it and are willing to listen to training suggestions (if only to be polite). If you don't have a background to point to then it might be a little more dancing around, and sadly some pet owners just never listen until both they and their pet have developed some really nasty bad habits.