There is absolutely positively no way to tell if you're seeing a "bad practicioner" after one session. Some proponents claim they can provide results in as little as 10 sessions, but the consensus is it takes 20 to 40 sessions to see profound results. This is entirely up to the type of neurofeedback being administered, the clinician and the client. Some people have more debilitating conditions that can't be tackled in 40 sessions where it's better for them to invest in a home unit so they can continue training more economically. Just stick with it, ask questions, do your research, then decide how good your clinician is.