First off, I’m not painting all salespeople with a wide brush here. Face it, it may be human nature for some to lack the conviction when they have a good bit of doubt about the anticipated customer's reaction to a proposal.
I'm not insinuating that most salespeople are lacking conviction when serving the proposal to customers. I am recommending that management discuss this with the team, that they must get their heads in the game at proposal time. They certainly need to be reminded that they are counted on to remain very assumptive so they can be influential on the customer's response to the proposal.