Forum Moderators: LifeinAsia
There isn't one single way.
First, there are lots of appraisal companies out there. I've seen several of their appraisals. These companies make their appraisals look professional and believable but essentially they make their money from stroking your ego (domain appraisals can give you valuations that are slightly more achievable, but only ]slightly). Get three appraisals for an established site, take the average, and list your site for sale at that price and you're almost guaranteed to never sell it.
The cliche is that a site is worth only what someone will pay. 99% of the time that's directly related to what the buyer thinks he can make out of the site (profit) and by when. Ignore that at your peril.
The best way of appraising is to put the site up for auction. Since you can set an undisclosed reserve this is probably the best way to judge interest.