Could have been his ~amazing~ smile

I'm pretty sure that's the only reason Dumbledore did anything

I always thought he just went
"There is now way this guys a death eater. Even they have standards"

Oh let a giant student killing snake roam the pipes, oh this will be hilarious

Dumbledore hired Lockhart to expose him for not actually doing all the things he claimed to do.

i think it's because he want to give a chance at anyone and to expect the best from other people

Didn't he say it was because it was hard to find anyone else who wanted the job? (because a new position was needed each year)

I thought Dumbledore would've fancied Lockhart like Molly Weasly...