I'm not too proud to admit that I can be a jerk sometimes. In the case of shutting doors you'd rather not shut, know when to apologize. Early on in my career before I learned not to burn bridges, I found myself doing a lot of apologizing and rebuilding relationships. Fortunately, I've learned my lesson, and the need for this in my own career has diminished.

We're in an industry that is built on solid relationships. Simply because the business relationship ends doesn't mean that the entire relationship ends. For example, there are several vendors that I don't currently work with that I still recommend from time to time. Certain publishers and vendors are just a better fit for different industries. Likewise, I receive calls all of the time from vendors and publishers referred from people I've worked with in the past, which is one of the biggest benefits of ending the active business portion of your relationships on positive terms. 

Keeping the doors wide open with every company and account rep by keeping your cool and agreeing to revisit business again in the future is the key to attracting business. By focusing on keeping people in mind, you're much more likely to keep your reputation stellar and have doors always open to you.