"My dear boy, ... do use your common sense. My books wouldn't have sold half as well if people didn't think I'd done those things. No one wants to read about some ugly old Armenian warlock, even if he did save a village from werewolves. He'd look dreadful on the front cover. No dress sense at all. And the witch who banished the Bandon Banshee had a hairy chin. I mean, come on ..."
"So you've just been taking credit for what a load of other people have done?"
"Harry, Harry," said Lockhart, shaking his head impatiently, "It's not nearly as simple as that. There was work involved. I had to track those people down. Ask them exactly how they managed to do what they did. ^Then I had to put a memory charm on them so they wouldn't remember doing it.^
... No, it's been a lot of work, Harry. It's not all book-signings and publicity photos, you know. You want fame, you have to be prepared for a long hard slog."

Never trust anything that can think for itself if you can't see where it keeps its brain.