Input-based or output-based decides the shape of everything
Before a single rate is calculated, an FM provider has to settle one question: is this contract selling resources or selling results? An input-based contract prices a deployment — categories, shifts, equipment, consumables, a management fee — and the client carries the risk that the deployment turns out to be insufficient. An output-based contract prices a standard, and the provider carries that risk in exchange for the freedom to organise the work.
Both are legitimate. The damage comes from ambiguity: a contract priced as a deployment and then managed as an outcome, where every service shortfall produces a demand for more people at no additional cost. Stating the basis on the face of the quotation is a two-line intervention that saves an enormous amount of later argument, and it also tells a client something useful about how the provider thinks.
