The specific fallacy being committed in this scenario is Begging the Question/Circular Argument. This fallacy occurs when an argument's conclusion is assumed in its premises, essentially arguing in a circle without providing any independent evidence to support the claim.
In this case, the speaker claims that ghosts exist based on personal experience ("I've seen them") and further asserts that their perception is valid because "ghosts are real." The argument is logically unsound because the premise (the person's observation of ghosts) relies on the conclusion (that ghosts exist) for validation. Essentially, the speaker is saying, "Ghosts are real because I've seen them, and I've seen them because they are real." This circular reasoning does not provide any clear evidence for the existence of ghosts, making the argument unconvincing. Instead of offering an independent basis for believing in ghosts (such as empirical evidence or reliable testimony), the speaker merely restates their conclusion.