First thing is domain name, if it is keyword rich. Second thing is traffic. Because your aim is to sell product using your domain. Third is backlinks and forth is pr. These all makes your domain really worth.
The domains are worth alot of you can build content and prove that you are unique. pay per click sites do not have real contents, mostly paid writers with keyword rich to get pay. The majority of the internet is PPC or parking. A domain is worth zero if it has no audience. AUDIENCe is the keyword.