"Moody" (Barty Crouch Jr) suggests this to Harry after he is almost caught out of bed in the middle of the night.
"You ever thought of a career as an Auror, Potter?"
"No," said Harry, taken aback.
"You want to consider it," said Moody, nodding and looking at Harry thoughtfully.
Harry Potter and the Goblet of Fire, Chapter-25, The Egg and the Eye
Considering the events of the night, Harry was completely fooled by fake Moody.
Harry walked slowly back to Gryffindor Tower, lost in thought about Snape, and Crouch, and what it all meant....Why was Crouch pretending to be ill, if he could manage to get to Hogwarts when he wanted to? What did he think Snape was concealing in his office?
Harry Potter and the Goblet of Fire, Chapter-25, The Egg and the Eye
Did "Moody"(Crouch Jr) suggest it only to lead Harry to believe that he was thinking along the right lines, and thereby throw him off scent from discovering his (fake Moody's) true identity? Or was it a genuine suggestion, based on a full term of teaching Harry DADA?
The latter doesn't seem likely considering Barty Crouch Jr was plotting Harry's death by the end of the year. But he could have just been doing his undercover job to perfection.
In either case, Harry does go on to reflect how ironic it was that it was a Death Eater in disguise that first put this idea in him.
My question is, was it an actual observation based on Harry's abilities (ignoring the murder plan), or was it a clever defense mechanism, by way of flattery, by the Death Eater to keep his identity concealed, considering his actual name had just been seen on the Marauder's Map?