Users as testers

Not every one who reads books wants to write books. Not every one who writes books read books from others. Not every writer is able to write in another genre and specialism. Not every one who wants to write books are good at it.

If this is true, why do we often expect users to start testing applications and trust on their verdict? Why do we rely on that outcome if we know we never told them what testing is and how to test. What we expect them to do?

I think it is because we trust them based on what they have shown. I also think a misperception is made based on wrong behavior. You can say that someone who performs one test is a tester with added value, therefore you can’t say: some user who performs a test is a tester with added value.
Sure, the users know how the system works and are able to tell what they do and how they have done it. Is this enough?

You have readers who are able to re-tell what they have read. There are also readers who are able to write a small review on that book. Still they are not able to write a similar book which attracts the same audience.

There are also writers who are able to write books for their audience. If they are asked to write for a newer audience they have to start learning again.

Can users be good testers? I think they can, only you have to be aware which value you are requesting from them. Don't expect a reader to become a writer in one day. Don't expect a user to be a good tester from the beginning. In both situations you have to guide them.

Also don't expect a tester to be a good user.