If a man refuses to let you watch his class he has something to hide. No one should ever be expect to put out money for a product they have never seen. What he has to hide most likley is that he is a bad teacher and his students suck. Being a good fighter does not equal being a good teacher. Either that or he's just a dick. Either way no watch = no pay.
I don't see what the problem is.
Just tell him you don't want to fork over any cash untill you see how they train. Thats a fair request.Find out when training is on and just turn up and watch a class. Its not like he'll kick you out.