How can one rigorously distinguish original Buddhist doctrine from superstitions practiced in various buddhist circles the name of Buddhism?

Given Buddhism’s long historical development across regions (e.g., Theravāda, Mahāyāna, Vajrayāna), what criteria can practitioners use to determine whether a particular belief or practice is: - grounded in early Buddhist doctrine, - a skillful means/expedient within a legitimate later tradition, or - primarily a cultural superstition layered onto Buddhism which is a deviation from the original teachings?