A review copy is a work order that will surely make you review whether being an article writer or ebook creator is really what you need to be doing with your life. Only give review copies out to select members who fit the qualifications that are likely to help your service (high post count, reputed members with lots of followers, thanks, etc...) and when possible, offer them at a discount instead of offering them for free. You do not want to strat your service out by showing that you are the bottom of the barrel, desparate, and easy to take advantage of.