If you look at the domain appraisals, people just post their domain(s) and nothing else. IMO, people are going to do the same thing, just post the website domain and ask for appraisals. Which no one will be able to give to them, because stats, revenue, ect. are needed.
If it does work out right, it will be nice... But you may need a form that has all feilds needed to accuratly appraise a site.