Corporations and Goverment: how do they choose an artist to decorate their buildings?

For all those corporate buildings of the big corporations and goverment, which are the guidelines to become their artist?
Corporations: Coca-Cola, Colgate, Procter & Gamble, all Ministries.
How can the artist become favorite of the corporations and goverment?

Governments adopt Committees and a panel selection process. THey may pay little to hire them; in fact teh artist simply gets teh publicity.

Private companies simply use artists who are famous, and have already made an impact /staement by their works. They may pay large sums to hire them.