Back when I was with Renebooks, the publisher used to just sent out a mass royalty statement with all of the authors in it, not single author royalty statements.  This allowed me to see what sold.  The average ebook is lucky to sell one or two copies a month.  Mine are back to selling 30 copies a week through various venues.

I’m not at all certain how I do this when others can’t.  I am not doing anything different from other ebook authors.

So where is the line in the sand that must be crossed to achieve sales?