The Chinese will tell them where to build, who is going to build it (The Chinese), how much they are going to borrow (from the Chinese) to build it and supply the trains.
They won't draw the Thais attention to the heavy penalties (not all financial, Hello, Sri Lanka, Papua New Guinea....) hidden in the contract for the slightest breach or default.
They sure as hell will try to gloss over the fact that control of the entity will be retained in Chinese hands.
All of this will be facilitated through careful bungs to the right decision makers.
Day by day, Thailand is drawn into China's sphere of influence.