There are verifiable proofs of improvement or attainment in the spiritual path. You will notice that person becomes happier because he has less suffering in terms of fear, anger, anxiety, depression, sorrow, grief, lamentations and despair. One can verify the improvement/attainment himself. It is also possible for others like psychiatrists or psychologists to verify the attainment.
There are no verifiable proofs of Enlightenment in Buddhism, according to the Early Buddhist Texts (EBT). When one has direct and personal knowledge of the truths, like personal experience, he knows he is Enlightened and has become an Arahant. A wise man can identify another wise man and also a fool. A fool cannot identify a wise man but often mistaken another fool as a wise man. Therefore, only an Arahant can possibly identify another Arahant. However, in the Vinaya rules for Buddhist monks, the Buddha does not encourage the practice of one monk verifying another monk’s attainment because this may be abused or misused for gaining fame.
Enlightenment requires abandonment of greed, hatred and delusion; it requires abandonment of attachment, clinging, grasping or wanting to possess. If a person is eager to receive verification on his attainment, it just goes to show that he is very far from Enlightenment. If a person is still seeking, that can only mean he hasn’t found what he is seeking. If one is eager to verify another person’s attainment, it just goes to show he has a strong ego, like standing on a moral high-ground to judge another. He is also very far from Enlightenment.
Some Buddhist sects practice verifying a follower as Sotāpanna, Sakadāgāmi, or Anāgāmi. It is contradictory to the Buddha’s teaching. The outcomes of various stages are described in the EBT. These are for one to evaluate himself on the attainment of the outcomes. Like outcome based education (contrary to input based education), one seeks to learn and attain the stated outcomes for self improvements and happiness. In original Buddhism, there are no exams or assessments to certify the attainment. No one should presume himself an Arahant to verify the attainment of another. Assessment methods created by modern society are not credible; it is like a certificate given by an unaccredited college. Exams and assessments can possibly evaluate the knowledge and understanding of Buddhist Texts but not the consciousness or spiritual attainment of a person.
Verification of Sotāpanna, Sakadāgāmi, or Anāgāmi requires the ability of an Arahant to read the person’s mind. If someone other than the Buddha says you are one-returner (Sakadāgāmi) or non-returner (Anāgāmi), can you really believe him?
Humans give animals a price tag in sales. An academic certificate is also like a price tag for one to sell himself to potential employers or customers. If you are not selling yourself, why do you need a price tag given by an evaluator? It is actually a humiliation to ask for a price tag, aka verification or certification of Sotāpanna, Sakadāgāmi, or Anāgāmi. In the EBT, the Buddha’s disciples never ask for verification but declared their attainments to the Buddha. There is also a Sutta where the Buddha taught venerable Ananda the methods for self-assessment of attainment.