When choosing a photographer, it is important to look at the quality of images they present. These days, cameras have very high resolution and are able to capture high levels of detail. Look at the images and determine if the photographer is able to take advantage of this strength or if they rely on Photoshop tricks to disguise their inability to adequately light and compose their images.
If you can go to a store and buy a sophisticated camera, why would you pay a photographer to do your portraits? Well, because the camera, no matter how wonderful it is, is still just a tool. A true professional is a master of their equipment, not just the camera, but the lighting equipment too, understands posing, is a master of lighting, knows how to make the best of any location, knows how to solve problems on the fly – and there will be problems. It is this expertise that you pay for. That is why you need to choose photographers who do in fact have this expertise.