I'm Not in a Hurry - This will only add stress to yourself when you think something is taking longer than it should.
Offering Contact Info - Contractors have people that they have worked with before and trust them to do the best job on your home.
Why's it so Expensive? - Contractors want to offer the best bid they can and still make money. After they have worked hard to do that, don't be insulting and ask that question. Do your research a bit so you know why something has more cost to it.
Complaining About the Weather - Weather can be a factor in a timeline of a job. They sometimes work in bad weather to get the project done and sometimes they can't. Complaining just adds more tension and stress to all involved when the weather is something no one can control.
I'll Buy My Own Supplies - Contractors work with certain supplies all the time and usually know what is a better product to use in most circumstances, what supplies are in code and a lot of times they can actually get a better price.
Let's Shake on It - Always use an agreement in writing. It will have all expectations outlined and if anything goes wrong, it protects everyone involved.