John may be sincere, but I suspect that he has an axe to grind . This means that John has a
Answer Details
The phrase "axe to grind" is an idiom that means someone has a hidden selfish motive or personal agenda behind their actions, even though they may appear to be sincere.
So, when we say "John may be sincere, but I suspect that he has an axe to grind," it means that even though John may seem sincere, he has some hidden selfish motive or personal agenda behind his actions or words.
Therefore, the correct option is "selfish motive."