Matthew 7:16-20 Ye shall know them by their fruits. Do men gather grapes of thorns, or figs of thistles?  Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit.  A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit.  Every tree that bringeth not forth good fruit is hewn down, and cast into the fire.   Wherefore by their fruits ye shall know them.

It's easy to tell the Spirit.  If a person says he is led by the Spirit to do evil, that person is a liar.  Don't take any instruction from that person.