Re: all of the functional requirements etc etc to have been completed and discussed up front.
The trouble is, as has often been observed, in order to be able to generate functional requirements and all the rest to a suitable standard t reduce the chance of failure to something small, you need probably need a sufficiently capable in house IT service that you don't need to go out and tender anyway.
Managing such contracts is an art in itself. The demonstration I remember was many years ago when my then employer had in house IT in a competitive tendering basis with all procurement responsibility devolved to the departments. The, shall we say Wotsits department's IT 'specialist', whose enthusiasm exceeded his practical ability by a very considerable margin, devised a tender with an amazingly complicated multi level client/local server/central server setup that would have solved all sorts of problems if it could have been made to work properly. However the complexity was such that the chances of it working properly in a reasonable timescale was about zero.
The in house IT department, being a bit naive about such tenders, said this will never work, and proposed a solution based on a central server with some very small local boxes doing nothing more than caching static reports. ICL (that's how long ago this was) won the tender with a proposal that very closely matched the customer specification, and complimented the customer lead on his vision.
Having won the tender, ICL then carefully managed the customer to accept a few minor changes to the system design. What these turned out to be were to increase the power of the central servers an reduce the role of the local boxes to caching static reports...
It was a lesson in the vital importance of customer management I've never forgotten. But think about how high risk it was. If the customer hadn't been sweet talked into, without realising it, completely abandoning his high risk design in favour of something practical then the whole project would have gone comprehensively and spectacularly pear shaped.