You have no idea what's involved in manipulating the metadata to fit 25 different retailers requirements and update the files every couple of days when necessary. (jakonrath.blogspot.ru)
Between the two different formats, various retailer requirements and a wide range of reading devices, there are many variables and restrictions to consider. (pressbooks.com)
If your book doesn't meet the Smashwords ToS, it won't meet retailer requirements. (smashwords.com)