What is the difference between a freelance marketplace and a dedicated development team?

A freelance marketplace gives you access to individuals who bid on your job, and you handle screening, management, QA, and cover for absences yourself. A dedicated development team gives you vetted engineers who work only on your product under a project manager, with shared conventions, code review, QA, and continuity built in. The marketplace suits small, well defined, one off tasks. The dedicated team suits anything ongoing or business critical, because it removes single point of failure risk and the hidden management overhead a marketplace pushes onto your internal team.