Until you present the proposal, you are in charge; you have the power. As soon as the Prospect has the proposal in their hands, you have transferred the power to the prospect.
In many cases, especially with hardware, the prospect trusts us to provide what they need. So they wait until they get our proposal and then use it as a guide to ""shop"" while we cool our heels. If the prospect is ""local"", we insist the proposal is delivered in person with a scheduled time of 1 hour. If I get there and the party won't/can't see me, I don't leave the proposal.
If the prospect is too far away to do that, we give a couple sentence statement for each of the Good, Better, Best Options based on Warrior's Standard Terms, Conditions, Schedule and Qualifications which will only be given out during final negotiations. The Prospect, of course, does not really like this but when we tell them we have a ""process"" that has worked for us and hundreds of other prospects just like him/her, and the process requires an in-depth review of the proposal, we don't really have a hard time with the followup call/meeting. Once you get to that point, however, the proposal needs to be top shelf.
The key is to keep control of the power as long as you can in the process. My 2 cents.