What to Prove at Court
This is a relatively complex question, however simply put; if you alleged something against another, then it is for you to prove your allegations. It’s not correct to say that this person duped you and then they conned others as well. The fact is if you charge another with a civil or criminal offence you are required to prove your case. In civil matters is on a 'balance of probabilities' and that assessment is from the mind of a reasonable person.
If, for instance, you claim that you were the subject to a misrepresentation and as a consequence of the misrepresentation, you want to be put back into a position you were in before, you will have to prove a variety of factors: that the statement made was untrue, that the statement would be believed by a reasonable person; that you are a reasonable person and did believe it. With that belief you then relied upon the statemen,t acted upon the representations and as a consequence you have suffered financial peril.
If you were told that by buying the car you would become 25 years younger you know that would be a falsehood and so would any reasonable person. If you joined a religious sect and you give all you belong to the acting prophet of the god, you believe in exchange for everlasting life, can you prove that that promise will not be fulfilled.