As I mentioned to John, the secret to profitability is NOT suddenly changing the rules, unless your main intent is to seriously undermine your credibility and destroy all that trust you've sought to built. The secret is creating brand-related content and product that your users, customers and clients are willing to pay for voluntarily, because they believe in your brand and wish to invest in it further. Those who are more interested in more brand-related content, my archives are also free. For those who are budget-challenged, but want to actively apply brand related tactics, there's a tape set for a few hundred bucks. After that, there's consulting and so forth and so on.
Free samples are just that.
If you don't have anything to upsell, that's likely where your problem is. They believe in you and want to further your brand. They already know that the more they invest, the more solutions they'll receive. Of course, first you've gotta have that brand strategy nailed down. Then you gotta follow it.