To expand on this:
>After the prescribed date, the bids are opened and assessed, and either the "lowest cost" or "most economically advantageous tender" is chosen. The contract award must also be reported in the OJEU and be published electronically on Tenders Electronic Daily ('TED'). [1]
It's difficult to choose the best offer if you are legally obliged to choose the cheapest one. This has led to a situation where all companies have to make cheap offers. The only way to make money is by invoicing bills for unforeseen work that wasn't covered by the original offer.
The irony of the situation is that there was an offer by the industry to build the airport for a fixed price. But Berlin chose to build the airport by themselves because that was supposed to be cheaper.
Well, Athens chose the other way: [2]
> However, after delays and slow development, the project was revived in 1991 with the then government launching an international tender for the selection of a build-own-operate-transfer partner for the airport project, with Hochtief of Germany being selected.
>In 1996, Athens International Airport S.A. (AIA) was established as a Public–private partnership with a 30-year concession agreement.[1] That same year, the €2.1 billion development finally began with an estimated completion date of February 2001. The airport construction was completed five months before schedule, but was delayed opening a month due to surface connections to Attiki Odos not being completed. The airport officially opened on March 28, 2001.
[1] https://en.wikipedia.org/wiki/Government_procurement_in_the_...
[2] https://en.wikipedia.org/wiki/Athens_International_Airport