What advice would you give a customer looking to hire a provider in your area of work?
It's much more important to find a photographer whose style you love.
You're not going to get a candid, journalistic-style shooter to shoot stiff, posed portraits very well; and a traditional, formal, studio shooter is not going to provide you with relaxed, natural, and candid shots of you and your family.
Love the pictures, then talk about price.
What questions should customers think through before talking to professionals about their project?
You don't have to pay photographers for your prints! They're your pictures, you should do what you want with them!
A "traditional" shooter will charge you a small (or sometimes non-existent) sitting fee to take the pictures, and then charge about $20-40 per "sheet" for prints. That means that (1) 8x12, or (2) 5x7s, or (4) 4x6s each cost $20-40.
A more "progressive" pricing model these days is to get paid well for your "sitting fee" and provide the edited, digital prints to the client, so that they can print them however they choose.
The one area that most people can't fulfill their own print needs is that of large prints, canvases, and albums. A good photographer can always help out with those, and at a reasonable price.