Saying no to a client can often feel like a crime, but saying yes and failing is actually worse.
We try hard to work closely with clients to avoid this, either by helping them plan potential work loads in advanced or through genuinely understanding the deadline and negotiating. Not all deadlines will result in Armageddon.
All that said, we are instinctively helpful people at Crush so will always want to, and try to help all clients at all time.
Thought this cartoon on Digital Synopsis sums up the biggest problem we face as an agency.