I haven't studied "NLP" much, but I've studied how it all works, mostly from hypnosis resources. CBT, NLP, and hypnotherapy all use similar approaches and can be explained by the same perspective.

Useful things I've done with my knowledge include pain control, phobia cures, motion sickness near-cures, helping people deal with intrusive thoughts, that sort of thing. All quite effective- not some years of talking it out therapy.

It's worth pointing out that "placebo effect!" isn't an argument against anything- if it works it works. It's just an argument for cheaper placebo's. However, the barman is not a skilled placebomancer, and neither are you unless you do your research.