People work a lot of angles if they are successfully violating their networks TOS with impunity. These types have a solid working model/method that makes bank, and they have the resources to protect it - including the information. If you are going to use established networks content lockers and even tread on the lines of possible TOS violations, you better know what you're doing or getting that money can be a real challenge.
Anyway, a content wall works best when the user KNOWS they are going to be sent to an offer wall. Typical examples might include standard CPA email submit offers often go to an offer wall by page 2. It can be almost seamless when integrated well, and many people just think they are taking the next step they are SUPPOSED to take. Another scenario where offer walls are effective is with PTC sites. Generally an offer wall works best when a reasonable incentive is offered, and the end-user ALSO expects to see an offer wall. That guy converts!