It doesn't surprise me. Most people described in the OP don't know anything about comics. At all. They know enough to do a quick search on Ebay and see a version of their comic selling for mega $$$ and assume that's what it's worth. They don't know about grading (for the most part), they don't know about CGC/slabs, very few get the concept of "second prints"... and biggest of all, they don't get that the SELLING price on Ebay is not what it is actually worth. I've tried to explain to some folks that I can list a musty rag on Ebay for $15k, but that doesn't mean it's worth that much.
Once some folks get an idea in their head, it's nearly impossible to convince them otherwise. Unfortunately, evidence is only valuable if the person is willing to accept it.
I've looked at a few Craigslist collections and known immediately that they had nothing but dollar bin dreck at best. Some get it, most don't. It is what it is.