The first-order checklist
Run through this before you click "order". Each item has prevented a real, expensive mistake for someone.
Measurements
Every critical dimension measured twice, with a unit and a tolerance, in a written spec.
Design
Parametric code in a repository. Exported file re-measured in a viewer against the spec.
Manufacturability
Checked against the shop's published rules. All upload warnings read and resolved.
Prototype
A plastic print test-fitted against the real object. Deviations fed back into the spec.
Review
A paid one-hour mechanical engineer review with written feedback.
Order
Quantity of one. Two quotes compared on price, lead time and shipping.
Money and rules
Landed cost calculated with finishing, packaging and shipping. Safety and certification requirements for your market identified.