Vertical: professional services — bill time, defend margin, sell the scope

Agencies, consulting firms, and creative studios sell hours and deliverables, not units. Their economics are unintuitive: revenue can rise while margin collapses, and the document that wins the work (the proposal/SOW) is also where margin leaks. Incumbents (Scoro, Productive, Accelo, Ruddr, BigTime — collectively "PSA", professional-services automation) model this correctly; a naive build does not. Spec against the real domain.

1. Domain vocabulary