We thought he was joking at first, but then we realized that he was 'in earnest'. [=he was being serious]
It's hard to tell if he's making this proposal 'in earnest'.
It began to rain 'in earnest' [='heavily'] in the evening.
(..) - Cocaine? - Would if I could find any. Mr. Luff... would you consider giving me a small advance in earnest of the day when the war is over and you can sell one of these with my name on it? I'm afraid I can't help you. Well, then I'm afraid... I will be forced to go to your competition. (..)2014 TvShow: The Knick Title: The Golden Lotus Season: 1 Episode 9