Holding a book promotion event is not necessarily a profitable idea. Though there is a direct relation between book launches/readings and book sales the connection is quite unpredictable. An author or publishing house can never say, "If we invest X amount in book promotions, it’ll convert in book sales." However, book promotion campaigns lead to book publicity, which might lead to higher sales.
A book promotion campaign could help if the statements you deliver are compelling. The communication you have at the book launch or book reading should be credible, should be in line with the crux of your book and should ensure that you entertain. Also you need to take care that potential readers remember your name or the book's title. Plus, your book should be worth the price.
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