1: Is the photographer of your choice really a photographer with training and qualifications, or did they just pick up a camera overnight ?

2: A good idea is to see a full range of the photographers work. Not just their best 3 frontpage images Is the photographers work consistent all the way through the images?

3: Are they a specialist in their field? A specialist tends to be passionate about their subject. If I wanted to shoot some interiors, I would prefer hire a photographer who specializes in interiors.

4: Every portrait photographer have their own style of capturing people. Some styles will date within a few years and some styles will look timeless.