Humans and dogs have very different greeting rituals which can sometimes cause problems, but you can teach your dog to tolerate, and better still, enjoy being greeted and it starts with understanding and skill building.
In polite human society we usually greet people, especially ones we are meeting for the first time, by shaking hands and making eye contact as we say hello. In dog-speak, however, such directness is at best interpreted as rude, and at worst, seen as a threat. Watch how two dogs greet each other when they're off the lead and you will appreciate how different the canine greeting ritual is and what dogs have to go through when a person, and in particular, a stranger, greets them.
It's almost impossible for people who like dogs not to go up and touch one on first meeting, and human greetings happen daily to dogs when they're out in public and when guests come over. While many dogs probably prefer not to be touched and handled so much, it is something they can learn to accept and even enjoy, so that any inter-species misunderstanding can be avoided.
Why should dogs accept human greetings?
Well, for one thing, it’s going to happen, regardless of your attempts to prevent it, so it’s safer for everyone if dogs know what to expect and are given the tools to cope with this weird human behavior. Some dogs are very social and like human contact but others will practice avoidance by jumping up, barking, growling, snapping or even biting if they're touched. The dog is then often blamed for telling someone what they think of their actions, even though the dog is entirely justified. You would do the same!
Put yourself in your dog's paws and think about how weird it would be if someone you didn't know came up and touched you without your consent. We don't even think about consent when it comes to interacting with dogs, but this needs to change, as asking for consent is vital. This would help us better understand and appreciate the position dogs are sometimes put into. So, while we can and should be better advocates for our dogs, teaching them to accept, tolerate and even enjoy being greeted is a 'muscle' that needs to be exercised.
Please note that this greeting skill should not be taught to dogs who are very nervous or who have a history of biting people until that is addressed. If your dog has bitten anyone in any context or is uncomfortable around strangers, please contact a certified professional dog trainer to help you. This greeting skill is for people-social dogs who sometimes struggle with these encounters and it's important to note that you should never FORCE a dog to greet someone if he doesn’t want to. He needs the freedom and space to consent to a greeting, but this cue can be used as a way to give him that choice.