You’ve seen 99¢ samples of toiletries in stores. For less than a buck you can know, unequivocally, whether it works for you. They make enough, and you’re out very little.
While the jury may be out on “taster” books for 99 cents, other industries provide a wealth of research. The food industry has known since its beginning that the very best way to connect an eater with food is to give them a free sample. Not only does this hook those who like, it weeds out those who don’t, without engendering bad feelings. It was, after all, free, or very nearly so.
The auto industry also knows the value of the test drive. “Try it before you buy it” is a time-honored practical marketing tool.
In none of these cases does the free sample, test drive, tester version imply a lack of confidence in the product. It’s simply the smartest way to connect the seller’s commodity* with the right buyers.
* Books, alas, are a commodity today. Unless we can point to a modern day Dickens or Camus, there is such an overabundance of books that a new author who thinks folks will line up to buy the first novel of an unknown for full price is in for a surprise.