Book advertising is difficult, and comparable to gambling. In book advertising, like Vegas, the House always wins, and you may, too, occasionally. Some ad runs are winners, and it seems, even more are losers.I've compiled the data from my book sale advertisements that I've purchased over the last two years. My goal was to focus on where my advertising dollars were best spent for 2020. Below is a table showing each online ad website where I purchased ad space for my e-book sales.One thing to note in looking at the data is that my books are young/new adult fantasy fiction, so I've targeted sites like Book Barbarian and Fantasy Book Reads that feature those specific genres. The data shows the advertising cost per sale. My books and sales prices varied from ad to ad, so this chart doesn't show profit or loss, just the advertising cost divided by the number of sales I recorded on the days the ads ran.The X-Factor which doesn't show up in book sale revenue is the earn…