Establishing What is Not Dhamma
Any teaching that has one or more of the following elements is not the authentic Dhamma:


eternalism (god or self or soul or world is eternal)
annihilationism (there is no self and nothing after death)
an independent, standalone and eternal entity or agent at the core of all experience (the self or the soul)
extreme asceticism
extreme sensual indulgence
does not contain the four noble truths
does not contain the noble eightfold path
promotes non-virtue (killing other beings, lying, stealing, sexual misconduct, intoxication, hurtful speech etc. - typical example is "waging holy war")
promotes wrong livelihood (trade in prostitution, slavery, meat, weapons, poisons, intoxicants etc.)


The authentic Dhamma is the opposite of the above.