Be sure to go see some of the contractors recent work.
Don't tell him how you want it done. Have him tell you how he is going to do it. The challenge is to find a deck builder you can trust. They should be insured and bonded. If a fly by night builder gets hurt on your property you will probably be liable for the medical expenses, lost work, etc.
You shouldn't have to pay more than a token amount up front. If its an expensive deck then learn about lien releases and use them to protect yourself. Be sure the builder pulls the permits (and not you).
Common problems I have seen over the years:
Fasteners not compatible with treated lumber, composite decking, and/or commercial hangers/brackets
Some composites don't like constant beating sun
Incorrect flashing to the house
Incorrect fastening to house structure
Posts for railings nailed to structure rather than brackets and approved fasteners
Jerks using pneumatic staplers rather than nailers
Jerks using pneumatic nailers and haphazardly nailing everything in sight
Building to minimum code
Building and not meeting even the minimum code
The guy giving the estimate doesn't do the work and sends the can't walk and chew gum at the same time crew to do the work
Remember code is minimum. Congratulations your deck passed with a D- grade.
Here is a PDF file based on the 2009 International residential code. I haven't kept up with what NC uses though. Deck code have drastically changed over the last 10 or 15 years. What worked even 10 years ago is marginal in today's world.
http://www.awc.org/Publications/DCA/DCA6/DCA6-09.pdf
There are various pictures and articles on the WWW about catastrophic deck failures. The higher it is off the ground the more a failed deck gets your attention.
Having said all that, I'll have to say building a deck isn't rocket science and many people can/do build their own. I've done more than my fair share over the years.
You just have to educate yourself and be willing to perform the physical labor side of it. Hauling the lumber to where you need it is a job for people a lot younger than me. I quit that heavy stuff when I turned 60 and don't miss it a bit.