gullible

/ˈɡʌləbəl/
adjective
  1. Easily tricked or fooled because you trust people too much.
    • Scammers often target gullible people who are looking for quick money.
    • He was so gullible that he believed the salesman's wild claims about the car.
    • My little brother is very gullible; I told him the moon was made of cheese and he believed me.