Over-promising is usually a result of a poor salesman who does not focus on maintaining long-term relationships with his or her prospects/clients (and will probably jump from industry to industry). Unfortunately this is rampant at businesses with high sales volume and lower software / contract prices because there is minimal incentive to focus on anything besides quotas.
If this happens often at your company, Client Services or Development needs to have a heart-to-heart with the sales manager.
Unfortunately, some of the most successful software vendors in the world have turned over-promising and risk-shifting into a way of life. For a million reasons, the market tolerates this injustice, and more often than not rewards it. It's hard not to be bitter about it.
If this happens often at your company, Client Services or Development needs to have a heart-to-heart with the sales manager.