Oops,

   I forgot to add that the software you use to make your items and what kind of items you're making plays into this.  Blender is quite popular now that the Gui isn't stupid and ridiculous anymore.  The workflow from your 3D app to Poser/Daz very much depends on your app.  There is a lot more information on creating clothing since that's so popular.  Making mechanical stuff that moves and/or has moving parts is harder.

I get the feeling that content creation is very much a dark art and those who have figured it out keep their secrets mostly to themselves,  treating the journey to enlightenment as a rite of passage.  I'm assuming that once my first item goes up for sale I'll be welcomed into the 'club', shown the secret handshake, and given a key to the secret lounge.