Why you are going to sell some site that is google adsense ready if you can able to earn that amount ranging $500-$1000 already?
It is just like commonsense why you are going to sell bigger money for small money?
Yeah right that's true why they are selling it if they can earn 500 to $10000 per month..
This is just like a marketing strategy or blackhat way to attract people to buy but the truth you can not earn that amount it is impossible unless if you made a blog that you runnning it for a long time ago and until now your blog still live and strong..