I'm just trying this out.
Imagine if you sent out a million spams, and you got back 900,000 answers that sounded interested, except that you just know that 99.9% of them are a waste of time? You'd think twice before repeating the exercise.
So, to people who have just bought a database with one of my email addresses on it that was scraped from somewhere 20 years ago and has been endlessly resold ever since, I'm replying with an expression of polite interest, but asking for a better price.
And they don't know this yet, but each time they offer a better price, I'll be telling them it's still too high. Until they get fed up with this game.