Ask to visit the references in person. Look at the inside and outside of the installations. Check mitering skills, look at how things are attached to the walls. Look for fillers. Be less concerned with design and bells/whistles and more concerned with the execution of the installation.

Then, google the addresses of the references and make sure that you are not visiting the home of a relative of the contractor. Check the contractor's facebook and see if he is giving you references that are also his best friends.

Make sure that the kitchens you look at are of the same brand that you are shopping for. Check the city to see if permits were pulled (anyone can check permits for any house, it is public record) and the contractor in question really did do the work.

Make sure the contractors have the right licenses for the work they want to do and that they have insurance and worker's comp.

My contractor, I later discovered, did indeed present homes of relatives as references.

You need to find out information about the subs used. Are they reliable? Was there any friction between the GC and the subs?
Were there any delays that could have been avoided? How responsive was the GC to your suggestions? Who chooses materials (doors, fixtures, etc) and pays for them? Was the work completed on time/on budget?
There are more, but these are a good start. (and you can see how my work has "progressed")

check BBB, Angie's List, and look at your state's online judiciary case site to see if they have been sued.

asking them which lumber yard they use, which plumbing supply, stone yard etc

Call each & see if the contractor pays his bills on time!

How did the GC handle requests for changes and what is the process?

What was the condition of the job site at the end of each day? (Especially important if you won't be moving out.)

Why did you choose this GC? What are his strong points? What are his weaknesses or what do you wish had gone differently?

Do you know anyone else who used him? (Maybe they know someone who used the GC but isn't listed by him as a reference. It would be interesting to find out why.)

We also tried to set some expectations with our GC about his subs, especially since we and our kids lived in the house for the first 6-8 weeks of construction for an addition. For example, we made it clear that the guys could not smoke in our house and preferably not in the yard (they had to sit in their cars if they wanted to smoke.)

Make sure and ask if he washes his hands after using the toilet :-)

Ask to visit a current project, and talk with that homeowner about how it's going.

We made the mistake of relying on (past) references from our architect, while he was in the weeds on three other jobs he was juggling when he took on ours.

Lesson learned.

Thanks so much everyone! I have scheduled a visit to a project that my architect and the top contender for contractor finished recently. I will use all of your good questions, and keep a critical eye out for the details.

My brother (a junkyard dog of an attorney) said he would use his judicial contacts to check the courts, and I can contact subs and lumber yards, what great ideas!

I am so keen to get my project to ground.

Semi: