Artists fix OBJ 3D models using software like Blender or MeshLab to resolve common issues—non-manifold geometry, flipped normals, missing UVs, or export errors. Non-manifold edges (shared by more than two faces) are cleaned with "select non-manifold" tools to remove problematic parts. Flipped normals (which make faces invisible) are fixed by recalculating or flipping them. Missing UVs (essential for texturing) are added via UV unwrapping tools. Export errors (like missing vertices) are resolved by re-exporting from the original software with OBJ settings that include normals and UVs.
