It takes time for a photographer to become an expert in their niche. For a specialist, it can take years of studying and learning in the field to become proficient in their photography. Additionally, they will need to continue photographing the same category to stay relevant and sharp. Imagine if a photographer was a generalist and focused on three or more types of photography. How long would it take for them, if at all, to become a specialist?
What if their portfolio looks great?
It is crucial that their photography style meets your desired image style. If their portfolio meets your requirements there is nothing wrong with scheduling with them. However, most photographers only post their best work and rarely will post anything they are not proud of. Additionally, there is bound to be at least one or two images from a project that is worth posting. I recommend asking the photographer to provide you with some of the images from their most recent projects. If their images are consistent, then they are likely to be consistent on your project. If their images are hit and miss, it is likely that some of the images delivered will not meet your quality standards.
To guarantee that the photographs that you invest in will meet your standards, I highly suggest hiring a specialist. Each photographer will have an area of expertise; striving to refine their craft to make it the best that it can be. With this in mind, they have likely been faced with many difficult situations in their career, and because of that they have learned how to handle what is thrown at them. With this experience in their pockets, a specialist is setup for success. Delivering you the best quality of images.