title_body: What guarantees that ebook/digital sellers are really paying authors per unit sold?
upvoted_answer: Ultimately this question is unanswerable because digital purchases involve an element of trust between content creator and distributor. 
  
  This is a real issue with the arts business, because fixed expenses by publishers  get tacked onto royalty calculations. Also, with creative content, budgets tend to be smaller, so there is less urgency for audits and confirmation. Smaller publishers also have less staff and infrastructure to do record keeping in a timely fashion. 
  
  But even with Amazon.com and similar kinds of companies, you can't really know. Amazon provides great reports of sales and royalties, but sometimes reporting is interrupted for some reason. Generally, though I have no reason to disbelieve Amazon's numbers. It's hard to imagine why a company like that would want to fudge the numbers -- though accounting software can be fallible or wrongly programmed. 
  
  Even with all the Amazon reports, it is rare that I as a small publisher have time to go over individual report. 
  
  I imagine that if you suspect foul play, an individual author can buy a number of ebook copies himself and compare against weekly sales reports. Obviously, that costs money, but ebooks are typically low-volume areas, so you probably could see sales jumps pretty easily.