dog does not eat dog
Nefarious people will not harm those who act like them. Naturally, that jerk preys on kind people and leaves people like himself alone. Dog does not eat dog, I guess.
Dog does not eat dog.
Prov. One disreputable person will not harm other disreputable people. Ellen: My lawyer did such a bad job that l want to hire another lawyer to sue him. Jane: You'll never find a lawyer to take on that job. Dog does not eat dog.