How do I believe that vampires are real?

Look him up historically. He really did exist. And yes the castle is in the Transylvania province of Romania. It's a bit of a tourist attraction.

Now you can say that you have talked to a distant relative a few times removed! 🧛🏻‍♂

They are kinda real in a sense. There's a medical condition called vampirism, in which people have a lack of iron in their system, causing them to feel fatigued and crave iron so bad, they develop a craving for blood; and not replenishing their iron levels can lead to serious health issues and even death. Nothing like how they're depicted in folklore other than having a taste for blood, but again, real vampires in some sense. 🤷‍♀

Are you asking why you believe that they are real? Or are you asking what could convince you to believe they are real?