Geometry:
No isolated verticesNo coincident verticesNo coincident/coplanar facesCorrect face normalsNo empty objects
Topology:
Quads and Triangles onlyModel can be cleanly subdividable
Other:
lighting and cameras are not included in the product (Model file includes only the 3D model)Model Scale: real-world scaleModel after 'reset xForm'Model centered at origin (0,0,0)all objects are named and logically grouped