After reading an earlier question which was marked closed as off-topic, ( Many sites propose free or cheap ebooks? Which are legitimate? ) I want to ask it in a different way.
What are some criteria for a consumer to determine whether a purchased or downloaded ebook file is legitimately bought and that provenance is verifiable?
Are there any methods or immutable file properties which could be used to show provenance?
If a publisher offers a non-DRM ebook for sale directly to consumer, what steps can the publisher do to reassure consumers that it it authorized to sell this ebook? (not just for today, but for 10 or 20 years down the road).
My first solution is to compare the author's website with the distributor or publisher website. But in some cases a publisher may authorize a company (like Amazon or Smashwords) to distribute through companies with different names in other countries -- sometimes the author or publisher may not know all the specific names of channels or might not have gotten around to listing all the sanctioned channels.