I was discussing Kickstarter campaign stuff with some people yesterday, and encouraged one of them to add an introductory backer level with relevant core books as digital rewards, for those people who are discovering their setting from this Kickstarter. My suggestion was to fulfill digital rewards for those backer levels every 24-48 hours during the campaign, simply by sending them a message with a 100% off coupon.
The question came up: "So they could download the files, then cancel their backing, and I'd get nothing?"
And the answer is yes. But what's the worst that happens in that situation? Someone gets your digital books for free. In my experience, a small number of people who pledge at that sort of level do it.
The realm of positive outcomes is much larger, though: at the least, they just bought something from you.
What's an even more positive outcome? They play your game. They read your book before your Kickstarter campaign ends, up their pledge level, and get a bunch of your new stuff. Or they go back and buy a bunch more things from your back catalog.
A single one of those positive results outweighs any number of people who pledge-download-cancel. Throw your trust behind your (potential) backers, and you'll all get rewarded.