government tender process

When top government engineers prepare estimates for a project, they do so based on actual construction costs.\nBut due to corruption, contractors bid low to do that work.When the government knows that the cost of a particular work is Rs 100, how can a person do that work for Rs 60-70, that too with profit?\nIn this also, the commission given to the government engineer Babu is not hidden from anyone.\nIn such a situation, how will we get proper, safe and strong construction?