My books are on Amazon, but I didn't know it was possible to even get any figures about how many samples had been downloaded, or in fact how many sales! Does that only work for the self-published on Amazon books?
Are these figures actually correlated on Amazon? That is can you tell if the person who bought the book had earlier downloaded a sample? So if 100 people downloaded a sample and 20 people bought the book, do you know how many of those 20 people were from the 100 samplers? Some people might just come along and buy it without downloading a sample. So the ratio might look like 20%, but might not be.
Others might download a sample, like it, but end up buying the book elsewhere.
Some people might download a sample more to act as a reminder to get the book later, than to actually read. I do that sometimes, with a book I already know I'm going to buy eventually. I get the sample and stick it in my To Read collection on the Kindle. I may never read the sample before I go and buy the book later on.
