Sometimes they can explicitly tell you what margins you can make in a Cost-Plus type contract. The thing is, when they dangle a 5-year long $75,000,000 contract in front of you, you'll basically take any margin at all since the amount is so large that companies will work to undercut each other drastically and even work at a loss just to get the past performance, which is treated as an asset (like cash itself) in the federal market.

They can also audit you any time they want to determine the "reasonableness" of your pricing based on overhead, margins, etc.