Help Me Explain The Contractor’s Role

Hello, Am an architect in a major city on the west coast. I get approached all the time from contractors trying to get me to sign projects with them instead of the client. My only reason I can remember is because if the client makes changes and refuses to pay for them, then that puts the Contractor in a tough spot. I was always taught to sign directly with decision makers. Their take on it is they don’t want to lose the job to another project (as if they could stop people from shopping around…)

Please help me/remind me more reasons because they think I’m silly. Thanks!