Be an RCP (Review Copy Pushover)
Given how "easy" I am about sending someone a review copy, have I likely been scammed out of a free book now and then? No question. But, to send out a review copy costs me less than $5 (including book, mailer, postage and press kit) for the very best form of advertising I could possibly use: the book itself. If I get even one actual bookstore/Amazon sale as a result, it's paid for itself twice over. If that sale is off my site, now we're up to a three-fold payback. Plus, another book is out there in someone's hands, with all that word-of-mouth potential.
And take it a step further. Even when someone hasn't asked for a book, think about why sending one might be a smart idea. A few months back, I threw an audaciously self-serving offer out in my monthly newsletter. Want some cards to spread the word on my work (for your friends, writers groups, etc.)? And had a few takers. Including a guy who ran a large writers group out west, who asked me if I'd like to be a presenter at their spring conference, all expenses paid.
from The Well-Fed Self-Publisher by Peter Bowerman (Fanove Publishing 2007).