The answer from Simon is correct, however, to counter the non-transferability of many online consumables, one typically receives five licenses for each purchase. This is useful (and I have verified it by doing this) if you have a family where each person has their own PSN account, on the same PS3, downloading the content with your "master" account and then logging in as another user and installing it with their XMB.
Thus, if you wish to also sell your downloadables and have the ability to do so, create your account on the blank PS3 next to your customer's account, download all your business once more, install on their XMB, and then delete your account. No problems.