The Spirit clearly says that in later times some will abandon the faith and follow deceiving spirits and things taught by demons. Such teachings come through hypocritical liars, whose consciences have been seared as with a hot iron.
1 Timothy 4:1-2//

One way to discern truthful teaching from demonic teaching is to find out if the teacher is a constant and consistent hypocrite without repentance; and, if they are a liar, which will likely be found out when investigating their hypocrisy.