I don't know if there is a definitive answer possible - after all, some of this is left up to interpretation. The confusing part of this for me is that I'm trying hard to do the right thing but, because things are so ambiguous, I'm finding it incredibly hard to understand what the "right thing" is to Google vs. the right thing is to Bing, etc.
Let's say that I sell a "training course". It's a video course - you buy it, watch it online, etc. It costs $5.
I can see that falling into one of two of the "Things":
I am the content creator (a.k.a. author/trainer). Why it's not a Product
It is a product, but it's a specific type of product - a "training course". A training course has an author, an instructor (who may be a different person than the author), chapters, subject matter, etc. Does Google lump "Products" in with "all widgets"? Dunno Why it's not a CreativeWork
On page, it can really only be one "Thing" and "CreativeWork" is ambiguous. Does Google think that a "CreativeWork" is a book? A movie? Do the minds at Google even think that a "training course" qualifies to be a CreativeWork? I don't know. I know that the Microdata page lists a "learningResourceType" but I can't find a lot of info on that.
I'm scared to mark it up as two "Things" - a "Product" and a "CreativeWork", for example. That would require either (a) duplicating a lot of things on the page (title, description), or (b) using meta tags that are invisible to users.
Any advice is appreciated.
For reference, here's the full list of defined "Things": [schema.org
EDIT: I goofed in the title - I realize that "Class" should not have been listed!