proof that a person really owns the real estate property

[Nilo Gabales Samson]

hello guys. i am still learning to become a real estate investor. i haven't started yet my first deal since I'm still on board the ship. just want to ask. one of my friend says he was talking to a seller then he wants to make sure that the one he was making deal with was the real owner of the property.. how can he know or is there any proof that the owner can prove that he really owns the property? sorry for this silly question. im still learning. thanks.