The entire Buddhist teachings can be summarized in the four seals (in the Theravadin tradition, it is more commonly known as the three seals). Anything that sounds Buddhistic but does not contain the 4 seals is not Buddhism. As such, the 4 seals are often used as a reference for people to distinguish what is Buddhism and what's not.
The 4 seals are:
1. All compounded things are impermanent. 2. All afflictive emotions are painful. 3. All phenomena are empty; they are without inherent existence. 4. Nirvana is beyond extremes.
(there may be other slightly different versions due to translation)
Read a very good teaching on the 4 seals from the following url:
Buddhism In a Nutshell: The Four Seals of Dharma - Dzongsar Khyentse Rinpoche
Yup, the Dharma seals are the best guide on knowing whether the teachings are trustable, in line with Buddha's teachings
An Eternal Now
The moment ceases as it arises, what the mind grasped is but an image of the ever changing Present. It catches the "Form", the "Enity", the "I" which is illusionary and misses the Essence. In reality there is no changing "thing", there is merely change.
Right at this moment is the display of the three Dharma Seals: impermanence, non-self, and nirvana, the emptiness nature all existence. This is the basis that every authentic teaching of buddhism must bear.
It is here that even the greatest mystic must take bow to Buddha. Such penetrating insight amid all kinds of lightning-fast changes to differentiate "I AM" from "Thusness".
The ever Presence of all cannot be something secondhand, it cannot be the object of observation. It remains original, new, clear and ungraspable. To enter into the profoundest source of our true nature, -to "know" Now.....Got to work NOW...