I would only accept a free session if the T or my counseling clinic was somehow at fault, or I had been deprived of something... for example one time I sat waiting for my T in the clinic waiting room for 30 minutes before she came out, apologizing profusely -- she was on crisis duty that day, and had been seeing a walk-in person who was in crisis. Because I only got 20 minutes with her, the clinic gave me my next session for free. And my T promised never to schedule me on her crisis day again.