I'll only comment on the contractual side: make sure you know exactly what you're getting for your money. Does the fee cover just his/her being there? Does it cover any prints at all? Does it cover a DVD? Is there a low res web site? Is there a high res web site? Does it cover an album? If so, what are its specs? What are the prices per print, and what size AND QUALITY (ours did her printing at Costco!)? Is there just one photographer, or is there also an assistant? What is the venue, so you and the photographer will know in advance if she needs any special equipment, and if so, what will the charges be? Is she insured? Who pays for broken equipment?

(Why am I pointing all this out: because we got...what's the right word? Surprised. Quality was great, costs weren't!)

Underlying assumption is that the photographer is good, but check out his/her web site, get recs from others, anything on Yelp, and maybe have them do some sample shots for you (engagement, around the wedding site, whatever).