The traffic to the site will generate leads for the company who owns the site. If they already have a website that converts then they will know what content to put on this site to create that conversion rate.
The buyer is buying the site knowing the potential that the site will have when it comes to generating business for them.
I've looked at is as the first page results of Google are a line of shops. The shop at #1 is seen as the shop which gets the most visitors to it. Now imagine that shop is currently being refitted - people can still see the shop and what it sells but are unable to actually enter the shop to buy anything.
Now, the person who owns the shop further down the street (i.e is ranked #10 or #12 or #15 etc) - he really wants to own that shop which is being refitted and he knows how much that shop is worth to his business if he owned it after the refit is completed.
Although the site I have created is a basic canvas, all it needs is branding by the new owner and it will then perform as well as their current site when it comes to conversion rates.
Does that make sense with explaining the view point I am taking on this project ?