First, Oedipus has a vested interest in not believing Teiresias. If Teiresias is right, then Oedipus is guilty of murder and incest, and he will have to face the consequences of his crimes. Oedipus would rather not believe Teiresias so that he can avoid these consequences.
Second, Oedipus is a proud man, and he does not like to be told what to do. He believes that he is the only one who can solve his own problems, and he does not need anyone's help. This pride leads him to reject Teiresias's advice.
Third, Oedipus is a suspicious man, and he does not trust anyone. He believes that everyone is out to get him, and he is always looking for hidden motives. This suspicion makes it difficult for him to believe what Teiresias tells him.
Finally, Oedipus is simply not convinced by Teiresias's evidence. Teiresias does not provide any concrete proof that Oedipus is the murderer, and Oedipus does not believe that the circumstantial evidence is enough to convict him.
All of these factors contribute to Oedipus's doubt about what Teiresias tells him.