We know quite a bit about the lives of average people, but of course, this is in sporadic incomplete chunks, dependent upon our available documentation for that era and geography, as well as the particular historiographical interests of the current period of scholarship.

For example, in the areas of former Carolingian Europe, you have charters, wills, deeds, laws as well as all sorts of other documents that have survived in church archives to tease out information about how the average person lived and worked.

In comparison, you have areas like Byzantine Anatolia, where almost no information of that type has survived, and knowledge about the lives of average people have to be guessed out of saints lives and the occasional tract of surviving Byzantine legal codes, like the Farmers Law.

And just so you know, historians (these days) rarely care "that much" about the veracity of an account, so much as what that account says about what was viewed as plausible within that world.

My favorite examples would be from an account of the life of Saint Gerald of Aurilliac, who lived in the 10th century. He was apparently a noble and chaste (they loved to stress this) saint. So much so that while staying at the house of one of his serfs (he was probably a count), he was saved from sleeping with the daughter of the serf by a miracle.

Did a miracle happen? Did the angels come down from heaven to save poor Gerald from getting lucky? Likely not. But we can tease out from this little nugget the fact that the author of this saints life thought it was perfectly normal in this world for an aristocrat to ask his serf to provide his daughter for "entertainment."

And this is how a lot of history is conducted these days. It's less about what "really" happened, and more about what people thought was possible, as real history is more than about the facts and dates of your high school class. It's about the totality of what can be gleaned from the past, in the way they thought, they acted, and they lived.

We know an absurdly large amount, more than any person could hope to understand in a lifetime, or several lifetimes. We also know almost nothing. It depends where you want to look, what you're trying to learn about, and how clever you are.

If you could narrow down the scope of your question, provide some context as to why you're asking it, or perhaps try to clarify what you want to know, I could possibly be of more help.

Also, just because something is written with an agenda it doesn't mean it's not very useful.