Softening a deadline

Always be sure to ask your client a lot of very detailed questions at the beginning of the project.  Most likely they won't be able to supply you with all the answers.  Then when your deadline is encroaching for whatever reason you can inform them that you are still waiting on the answers to your questions.  The client will understand that the deadline needs to be moved and won't be upset because they will realize that the responsibility falls on them for not supplying you with enough information.