When hiring a wedding photographer...
There is a lot to do when shooting a wedding, and it is important for the photographer to be a step ahead of the next shot. Wedding photography demands being on your toes, running with the action. It requires knowing when and where to use external lights (flash photography) and ability to switch back and forth.
No matter what, even if your wedding will take place outdoors, a flash is necessary.
Be wary of photographers who advertise themselves as "Natural light Photographers" because often times, it means they're not familiar with using a flash. Also be wary of portrait photographers who say "sure, I can shoot a wedding." Capturing weddings is a skill in itself, a skill acquired from shooting many weddings. Wedding photographers know when and what to capture. They;re usually wonderful portrait photographers as well, and understand the special demands of shooting weddings.
A good photographer should be in touch with you several times prior to your wedding to exchange important information like the schedule of events, rehearsal date, etc..
And by all means NEVER ask a friend or relative who happens to have a "nice" camera if they wouldn't mind. A non-professional is never a good idea, no matter how many beautiful sunset photos you've seen. Plus that guest will not be able to enjoy your wedding!