Unfortunately, the ethical implications of this would be troubling. Refunds would have the effect of reinforcing whatever the patient did that session. If doing or making up wild stuff is what gets you a free session, some people are going to realize that. If other patients catch wind of one person getting a refund, they may end up doing and saying wilder things, too. Patients' best interests would take a backseat to the entertainment of the therapist, and that's pretty messed up if you think about it.

Yeah, ethical therapy person gotta ruin the fun. Sorry guys. But there is potential in a refund model. It could go far if it's used to reward positive things, like putting the most effort into working out an issue, or making the most personal growth over a period of time.