Relation between Sales men, Process and project delivery

Is there any relation among sales men, Process and project delivery. Whether you agree it or not, I strongly see a relation here. Consider a scenario where, the sales person bids a project for a software organization, and gets the project. Now, the job of the salesperson is over, and the next step is for the delivery team to take responsibility and deliver the project on time to the customer.
As we are aware, project delivery is controlled by the scope, time and cost. Any change happening to one or more of the parameters has impact on others. If the time is committed to the customer as in fixed bid fixed time project, then we need to ensure that scope and cost are also in line. If the sales person has gone and committed a particular time line to the customer making assumptions on estimations, it is going to directly impact the delivery and the developers have to go through terrible stress (assuming he is over committed) during implementation.

Let us talk about the impact of above two parameters onto process. Let us take the project following agile methodology. Estimation in agile projects is done using IEH(Ideal Engineering Hours). In the projects I have seen, IEH is anywhere from 6-61/2 hrs per day.
What if sales person is not aware of the IEH and sells the project with 8 Hours per day in mind ? Who will work that extra 1 1/2 hours committed by the sales person ? How do you compensate for this ? I know that you know the answers to above questions !!!!