After you narrow down your list of possible photographers to your two favorites, request two or three references to help you decide between the two. If you ask the photographer for a list of references from prior clients and they are hesitant to cooperate with your request, immediately cross them off your list because it is suspicious that he or she is hiding something, perhaps a poor job on his or her part.
After you obtain the references, call the numbers and ask the former clients if they would feel comfortable recommending the photographer to their best friends. After they give you their response, ask them to explain why or why not so you can see what they did and did not like and if this matches with your expectations. Also find out if the photographer was on time, well dressed and completely professional during the entire event. If the prior clients had guests make comments, were they positive or negative? The answers to these questions should help you make a more informed decision between your favorite photographers.