As others have indicated this is a difficult area. I've done a quick scan of the literature and most of it is about setting up a robust complaints system and then ensuring that potential complainants feel confident enough to use it. However, overuse of the complaints mechanism does seem to be a problem in some countries/regions: Kenya comes to mind.
China operates a 3 counts and you're out system: if three complaints are made and no convincing evidence is found then the complainant is blacklisted. If false complaints are found then a complainant is blacklisted straight away and criminal proceedings may follow. If this is how it is done in China, my gut feeling is that this is probably not the way to go, since it seems like more complaining might have saved a lot of money (according to the FT, Chinese academics have recently estimated that as much as $6.8 trillion may have been wasted on public 'investment' since 2009 -
http://www.ft.com/cms/s/0/002a1978-7629-11e4-9761-00144feabdc0.html).
Apparently, in Denmark there is a small charge for lodging a complaint. In the UK, there seems to be no dedicated procurement complaints mechanism and any complaints must be pursued through the civil courts at huge expense to complainants, which is a huge deterrent. A recent example is the flawed award of the West Coast Main Line franchise, which went as far as a parliamentary select committee investigation:
http://www.theguardian.com/business/2012/oct/03/west-coast-mainline-franchise-key-datesThis is not the kind of process that small players can instigate and, as in many things PFM-related, UK practices are probably not for everyone!
In Georgia, the approach is entirely different: anyone, even parties with no involvement, can halt a procurement process at any time as described by Transparency International:
'Anybody who detects a potential violation of the law in an electronic tender process can file a direct complaint on the official procurement website, which is then reviewed by a Dispute Resolution Board, in which TI Georgia is represented, within ten working days. This online reporting mechanism is a very innovative approach that allows the public to scrutinize public contracts and to take action and stop a process, if they find violations of the law.' http://transparency.ge/en/node/3117The Georgian system is not perfect as the TI review indicates, but paradoxically this very open and responsive complaints mechanism does not seem to have resulted in the system becoming bogged down in malicious complaints.