It is very hard, if not impossible to tell a bad martial artist, a bad master, a bad teacher. Unfortunately, tragically they wear no sign!
Before making a commitment, whether to a person, for example in a personal relationship... or committing to a new hobby... spending ones time, energy, efforts to make said thing work... caution is required. Start carefully, and see if their words match their actions. Does some claim sound too incredilous to be true...? Do you not like the vibe from that person?
Follow your gut feeling.
Whatever you do, NEVER, ever be alone with them, unless you are 10,000%certain that you trust them. When and if you do, you are an adult, and either consent to XYZ or do not. Cheap Trophies are $10. Just because something is written in a foreign language does NOT mean "my certificate" of prowess says what I claim it to be. Talk to other adults in the program. Talk to lots of people. Watch carefully what is being taught. Is that atmosphere a place in which you will be comfortable? That particular approach to instruction one you value? If not seek learning elsewhere...
Sadly there is no easy blanket formula for detecting the pervert, the fraud, the criminal. If you can encounter anywhere else in the world then you can find them in the dojo
, either as a student or a teacher. Caution is the rule.
Buyer beware... always,