A certificate or diploma is the best way to identify a qualified healthcare professional.
Promising a cure before examination is incredibly impossible, not to mention unprofessional
Avoiding the topic of qualifications is sketchy. It often means that they're insecure about them, or is trying to hide something.
Offering a secret cure is just straight up dodgy. That's the trademark sign of a "snake oil salesman." Meaning, the "secret cure" is either a placebo, incredibly experimental, or incredibly dangerous.
One of the main ways to know if a health care professional is legitimately qualified is through certificate, diplomas or similar documents because these prove the professional participated in educational programs that train appropriately health care professionals. Also, a diploma or certificate in specific areas shows the professional has knowledge and experience to provide treatment for certain conditions, give recommendations to patients, etc.
On the other hand, that a professional promises a cure, offers a secret cure or does not talk about qualifications might be an indicator that he or she is not qualified as these are non-professional behaviors. Therefore, the one that can help identify a legitimately qualified health care professional is a certificate or diploma.
