By providing something of undeniable worth to the recipient, you raise their estimation of the worth of your offer. When people are offered free samples or even full-sized versions of a product, they feel like they are getting a great deal. And as a bonus, they’ll probably keep using it, as product ownership tends to increase appreciation. Potential users, for instance, risk giving up a great resource once a free trial period is over. For instance, “$20 free play for signing up” or “Try it for 14 days for free.”