There are three simple but fundamental questions that we can ask, to learn whether a spiritual practice is true of false.
1) Does the practice aim to enslave you or to set you free? Are you expected to labour as an apprentice for ever, or are you expected to become a real master of yourself and so liberate your true spiritual being?
2) Does it give you control over the whole of your subtle system? Not just a sensation here and there, or a limited set of spiritual powers, but a complete, interlocking and verifialble toolchest of techniques and guidelines which deliever consistent results every time you use them?
3) It is a business? Are you asked ot pay money to progress in your spirituality? Is there a hierarchy of practitioners, and a document which claims to certify your ability?
Real yoga (union with Divine) does not seek out celebrity practicioners or try to glossily market itself to entice more followers. It is not trendy or fashionable, is not sold through smart advertising and smooth talking sales pitches, does not charge significant sums of money for progress to new levels of experience, does not promise enlightenment for a fee.
Real yoga comes from the ancients forests of time. It is differencial, humble, quiet and hard working. It makes no promisses and tells no lies. It has no quick, glib answers, nor does it sell itself with slick organisation and designer brochures.
Real yoga is within you, locked in your subtly system, and when you find it, it is your success that is the triumph, not the form of yoga or the Guru that took you there.
Self knowledge is the gift at the top of the tree, the ultimate personal achievement.