I wish there would be a way to tell is model solid and whether there are reversed faces before downloading

Two advanced filters for models would be helpful:

  1. Model has reversed faces or not;
  2. All components are solids or not.

I guess all of it could be automatically evaluated for any model.

I think it will save man-years of time for the community.

It is problematic. Usually a well built model is not a single blob of loose faces and edges, but has parts. If you build a model out of solid components and groups, SketchUp won’t see the result as a solid even when geometrically it is all right.
There still doesn’t exist a foolproof algorithm that could detect reversed faces. The best device for this is the human eye, especially when the elements are not solid.
Some models need not to be solid. It is often desirable that everything in the model that is not seen in normal circumstances has been removed to reduce the amount of faces and edges.