Think about it. How does a commissioning editor get to be a commissioning editor? It's usually not because they've been, say, middle management at Marks and Spencer. No, they've come through the ranks. Many have had stints as booksellers or been agents (or their assistants) en route but essentially, at some point they'll have been the one making the tea and going out to get the sandwiches.
Those people are usually the ones who new authors first make contact with at a publishing house or agency. So a new author would be advised to be polite and considerate at the very least. You may be thinking you always are, and I expect that's true, but there are some people who phone up demanding this or that, or respond badly to rejection and take it out on the assistant. Not a good idea because, remember:
The Tea Makers of Today are the Commissioning Editors of Tomorrow.