Why should the study be credited against the mandate?

Because a study that is never paid twice cannot be a sales tool. If the fee disappears into the mandate on a go, the consultant earns nothing extra from a go, and the recommendation can be read at face value. If the study is priced as a separate profit centre, the owner is right to wonder whose interest a go serves.

From Should a Feasibility Study Be Credited Against the Development Mandate? What a "Stop" Costs and What a "Go" Buys — the full reading, with the method behind this answer.