#3) Be cool.
It’s hard to believe–I mean, what’s cooler than a ninja?– but ninjas were not respected during their time. They were, basically, the scum of the earth, about as low as actors or beggars or people who handled corpses for burial or cremation–all of whom had a hard time of it in feudal Japan.
How could somebody with the skills of a ninja be looked down upon? Well, the warrior ideal in Japan at the time was the samurai, riding boldly into battle, challenging a foe to single combat, preferring death to dishonor, etc., etc. It would have been entirely beneath a samurai’s dignity to sneak about in disguise, to knife someone in the back, to lie, to spy, or to steal. Which is why samurai and warlords hired ninjas to do these thing for them.
It would also have been shocking for a samurai to accept payment for fighting, or to serve more than one master. Both of these were things that ninjas frequently did.
So ninjas were despised in their day. But also very useful.