Does tender system/Auction system work well in public works?

Tweet

Government contracts are a lucrative source of income to Equipment suppliers and Construction Companies. Usually tenders/bids are invited and the lowest is accepted, to show that proper systems are followed. Verification of technical competence and past experience is also counted. Some bank guarantees are obtained for due performance. Yet shoddy work is done, and the lives of people get endangered owing to defective bridges and buildings. Why this happens?