Much of the time sales' over-promising comes as a result of some management or client services functionary that's not a technical product manager but thinks they are insisting that $requirement definitely will be possible once $feature is in place, which definitely will be on time, so no need to communicate with the dev team at all on that.

(It's often the same middle management that omits to let the dev team know the system is supposed to work on IE8 until the client complains.)

Sales commmonly direct their sour taste towards the developers...