The idea of teaching martial arts in this forum is not profitable and waste of time, because there's a lot of materials training can be found outside in this forum. Ex from YouTube .I think it's not worthy to use Bitcoin as payments to martial arts instructor like you. As you said martial can be learned without a Trainor.
He will not lose much effort and time to publish about his services in a cryptocurrency marketplace as he adhere to forum rules and require btc payments. The forum is not only dedicated for digital goods but opened for all kinds of online services.
Btw, it's always great seeing people offering all kind of services in exchange for bitcoin. Who knows, maybe his initiative would be a motivation for other to start accepting btc payments for their services.