Answer:
Well sometimes there so ridiculous you can just tell if its legit or not. In some cases, it can be hard to tell. Although sometimes questions may seem plausible. You can prevent this by simply just doing a quick minute of googling, just to be safe. Some remedies can be partly true and some can be completely trust-worthy. In all scenario's doing research is the safest way of deciphering whether a remedy is helpful or not.
Another way to determine if a remedy is legit or not is speaking with your doctor, it is not as quick as researching but it is still safer than trying it. You can also just ask someone you have tried it. If someone you know happens to have tried the remedy.