NOT to buy. And that's exactly what we're trying to avoid. I don't mean to imply that you should have NO free information on your site, but use it in moderation. And, let whatever freebies you DO offer be a means of leading to income for yourself. For example, if you have an extensive library of self-authored articles, offer reprint rights to those, and add to it regularly.
Online marketing is all about testing, and there's no harm in trying new strategies.