Once you've narrowed down your photographer choices and are arranging to meet with them to discuss your plans, make sure you're meeting with the person who is actually going to be photographing your wedding.
This may sound obvious, but larger studios and companies may have multiple photographers and, even if you meet one of the photographers and not a designated "sales" person, it may not be the same photographer that will turn up on your wedding day.
I'm a one-man-band, so it will always be me that answers emails, answers the phone or turns up to meetings. And its always me that will be there on the day, and that edits, processes and prints your photographs.