Suppose it's the 16th or early 17th century, and I want to publish a book/pamphlet/etc that I wrote. Where would I go? What criteria would the publisher use to decide if my book is worth printing? Where/how would my book be sold? How would I get paid?
At that time there was a few different routes you could go as an author with a manuscript. Either you could persuade a printer to buy the manuscript, or if you were mainly interested in getting your book printed, and less interested in the money, for him to be gifted the manuscript for printing. In the first case the author would recieve a fixed sum, and that was it. In neither case would the author recieve any profits from the sale of individual copies of the printed work, since they had relinquished it to the printer who would be responsible for the sale and all income from it and in effect owned the work (this didn't prevent pirate editions or translations being printed by other publishers, without the original publisher getting any of the profits, of course).
It is obvious than in this scenario the printer would mainly be interested in whether the book would sell. So that is also what they would consider when deciding whether to buy the manuscript in the first place. Then as now there was really no fixed formula as to what made a book sell, they could only go by current trends and educated guesses, some more educated than others (literally speaking, as some printers/publishers were educated men, others not). Some publishers speculated in scandal, others in solid but uncontroversial sellers like religious books or text books for nearby universities and such. It could vary greatly from publisher to publisher, and they could go bankrupt very suddenly from bad business decisions just as any other artisan or merchant in the period.
The other route would be self-publication, which meant that the author would have to pay the printer for the expenses of the entire printing run. For a wealthy individual this would not be a problem, but most authors of the period was not wealthy, so this was mainly done though patronage. You could dedicate your book to a wealthy and influential person, like a noble or a monarch, and they would in turn provide money for publication and perhaps a bit extra for living expenses and such. The author would then also be responsible for the sale. If it was a learned person they could perhaps rely on a network of other learned persons to take copies in commission which they would sell for a percentage, or they could perhaps persuade local booksellers to take over part or the entirety of the printing run, but again either for a commission or for a fixed sum.
In the later 17th century and the 18th century a number of commercial developments occurred in the book market, such as the invention of subscription and serial publication, both of which made it more easy for authors (and publishers) to publish books without having much of a start capital, as well as the rise of something akin to more modern publishing firms, who could pay authors more for their work, and in case of "bestsellers" also pay them for extra printing runs and copies sold.
These developments made the life of an author more profitable than it had been in the 15th and early 16th century, but it wasn't until the 19th century that the actual publishing practice of authors being paid for copies sold and retaining rights to their manuscripts and other such things became common practice. Until then literary work was mostly not very profitable, and the examples of such authors as Alexander Pope or Voltaire, who became very wealthy by not only being succesful authors, but also their own publishers, remained exceptions to that rule.
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