Start clean
Use a new scene so existing units and objects do not hide problems. Import and note model size and orientation.
Measure scale
Add a reference with a known dimension and inspect numeric transforms. Plausible-looking models can be wrong by factors of 10, 100, or 1000.
Inspect topology and normals
Enable face orientation. Look for duplicates, thin triangles, disconnected islands, and negative mirrored scale before recalculating normals.
Check UVs
Use a checker image to reveal missing islands, stretching, unwanted overlap, and reversed orientation.
Test downstream
Export one representative asset before a library. Record axis, scale, smoothing, tangent, and FBX-version settings.