As a regular buyer of sites, some of them from here in DP, may I say that it is not atall important fir me as to why a person is selling the site. The honest answer, "for the money" is quite rare in a reply to that question in any case, with "have no time to run it" being the popular response. For a buyer the two most important questions, which should be the first two in the list, would be what the website does and why is it better than the competition.
It is not clear to me what you are suggesting regarding the operation of the DP Forums. Are you suggesting that a new Section be put in place to discuss the topic of buying/selling websites?
Not atall. Simply add a couple of questions for sellers, before the "why am I selling this site". First being a very brief description of what the site does. Second, why it is better than its competitors. The above information is universally provided for any product or service for sale.