There are many difference between a professional photographers and just an amateurs. For starters us professionals know a hell of a lot more about lighting and posing than amateurs. We also understand that we are trying to be a professional business, therefore we hold ourselves at a higher point. We create photography pages away from our personal social media accounts and separate out personal lives from our businesses.
Most professionals have awards and recognition of some sort from other photographers or photography associations as well, some may be starting up but if you truly want a professional you should find someone who has had some experience. Even visually you can tell who is a professional and who isn’t, composition, lighting and color is a big indicator on who knows their stuff and who doesn’t. Even in my early stages of photography I was definitely an amateur, my angles were odd and awkward and my lighting was always either too light or too dark.
Another difference between the two is their equipment. Professionals spend thousands of dollars on lights, cameras and difference printing essentials to ensure their photos will be the best quality.