Many martial arts fakers teach unrealistic and often foolish techniques. For example, it's good to learn how to knee an assailant in the groin, but it becomes instantly dangerous if they claim that these techniques can equip you with the skill to overcome multiple attackers.

You should be aware in what discipline your instructor trained. You want to take a self-defence course at a martial arts school that offers instruction in a specific discipline.

The goal of being prepared for self-defence is different from training in a specific martial art. Yet, learning a particular style might equip you to apply your skills if necessary.

Practical experience or years of training in a specific self-defence style, whether it's Judo, Brazilian Jiu-Jitsu, kickboxing, karate, etc., is the best way to become prepared for a dangerous situation.