How do I found out if a book or author is really a best-seller?

Congratulations on finding the Holy Grail of writing!

I’ve taught literacy to learning-disabled, and we were warned that our students would “never get to the point where they can get lost in a book”… I said “THAT is the saddest thing I’ve ever heard.”

Of course not. Sorry if I seemed to imply that anyone had. I’m just expressing surprise at how many authors I’ve been running across lately that seem to be succeeding (for certain values of “success”) despite not composing very readable prose.