There are many factors that influence how a dog responds or interacts with a person whom they have just met. Here are some of them:
Build of the person
Some dogs yield submission to people who are tall and large. They do this even if the person did not give a command. But some small, timid, or nervous dogs can become more hesitant to interact with the person compared to when they are facing someone who is more petite. If you are tall and/or have a large build, crouching or sitting will enable you to get down to the dog’s level.
If you meet a dog for the first time, make an effort to slow down your movements. Smooth and gentle actions can help the dog relax; and it can increase the possibility that he will see you as a friend rather than a threat. This is one reason why heavy-footed people or those that use a lot of body language or those that move quickly may appear more overwhelming especially to shy dogs. To seek professional help, pay a visit to your nearest animal clinic.