"Fair price" is a vague term , what might seem fair to you might not seem fair to others.
The only price you should be concerned about is "Market Price" , Market price is at what price range a particular model of car is selling.
It doesn't matter if you think the "fair price" of a 2020 Civic is 3.5 million , if market price of that car is 4.0 million , no one will care about what you think as fair price.
And believe me , no one will sell their car below market price even if they bought their car lets say 5 lacs cheaper brand new 2 years ago
So either you buy at market price or go for new .