The lack of primary sources wasn't the only problem. Two of the curriculums that I looked at (the titles and authors of which shall remain nameless) made a big impression on me--and not in a good way. While scanning the pages, I noticed several typos in the chapters. One author confused the word "throne" with "thrown" and even made the egregious error of stating that the people "sang hims of praise."
I was a little appalled that an error this blatant could get into print, and especially into something that was being marketed as educational curriculum. It also made me think: if the author did not take the time to check his own spelling, what was the likelihood that he had checked his historical information? Were his chapters all based on one book he had read, ignoring the multitude of other sources available? Did he even look at the primary sources while performing his research, or was he merely regurgitating the popular view of history as told in (outdated?) secondary and tertiary sources?
In short, poor orthography leads one to suspect poor historiography.
For self-published authors, the same rule applies. A poorly edited historical novel can lead one to suspect that the author doesn't really know her stuff. Who is going to trust an author's scholarship or stay immersed in a novel's storyline if the author clearly can't tell the difference between "then" and "than"? Editing: if you can't do it yourself, then find someone who can.
And now that I've rung such a peal over bad spelling, I suppose I'd better proof this post nine or ten times before I publish it. I wouldn't want to make the same misteak that I've just been complaning abowt.