Dumbledore’s shady hiring decisions

We all know that to teach at Hogwarts School of Witchcraft and Wizardry, you had to be an amazing witch or wizard, which is why some of Dumbledore’s employment decisions were dubious.
Why did he appoint Professor Quirrel to teach Defense Against the Dark Arts while he was terrified of everything? Why did he hire Gilderoy Lockhart, after all? Dumbledore must have been able to see through this thief’s lies and deception. It simply does not add up.