My first few attempts at uploading models to SketchFab were not overwhelming successes.  There is not a one-to-one correlation between what a model looks like in Blender, especially rendered in cycles, and what it will look like in SketchFab.  Like most things, it's a matter of understanding how to prepare the model in Blender to make the transition as easy as possible.  This category of my blog chronicles the baby steps I'm taking. :)