I have a doubt here, well, when a person registers for adsense program, initially he gives his website link in the registration form, and what if another person buys the sites and registers for adsense?! he will also give the same site link during the process of registration..?!! then it will look like two people are trying to register adsense account with the same website.. do you think its possible?!!! wont there be a problem during the registration process...?!!
I think it is possible if it is a while later. If you register with a site and then a few days someone else registers with the same site that will be flagged but months later should not be a problem. Google is aware that sites are bought and sold and they often just look at the content of the site when approving. Be weary though if the owner of the site was banned from Google because they may think you are trying to start a second account.
This may not be what you're asking, but you can put two or more different AdSense ID's on one site. My partner and I both have our ID's on our sites and that doesn't seem to be a problem. Certainly if you sell your site you're going to want to change the ID to the new owner's AdSense ID, so I don't think Google would have a problem with that.