On fixed-price contracts, however, companies can pull in 20-25% net margins sometimes. The average net margin on all contracts is between 8% and 12%. You can verify this by looking at the financials of the publicly traded contracting firms like Booz Allen and Leidos who are all in that 8% to 12% net margin range. There is no limit on these margins set by the government, however, just guidelines on what is "acceptable" to them to be included in your pricing (costs and profits passed on in the form of billed fully-loaded labor rates for hourly work).
It's actually more profitable for companies to do contractor-facilities (remote) work on a fixed-price basis, contrary to what people outside of the industry think.
The only time this (high margins) really happens is in the no-bid cleared (black ops) type contracts let by the intel community and such. Those margins can be huge, but it is because of the level of clearance and company expertise required to perform the work.
However, even in that case, it's not 10x. Maybe 30-40% margin, but not 10x.
Why? If anything, it should be a violation by the department to pay x10 times for the same work they could get by going directly to the subcontractor.
They can also audit you any time they want to determine the "reasonableness" of your pricing based on overhead, margins, etc.
If they would have had taxable earning anyway, it doesn't matter.
(Of course, that's from a purely economic point of view. We are talking about politics here.)