How to know if an activity is right or wrong

Devotee (1): If someone has a desire to do something so that…
Prabhupada: Do something for Krsna?
Devotee (1): For Krsna. But he begins to realize it’s still tinged with a
lot of personal gratification…
Prabhupada: Therefore he should consult spiritual master. The guide is
there. Then it is all right. He should take sanction from Krsna or Krsna’s
representative. If he wants to do something, that’s good, but whether that
doing is right or wrong you have to know it from Krsna or His
representative.
>>> Ref. VedaBase => Srimad-Bhagavatam 6.1.15 — Auckland, February 22, 1973