A lot of things people place great value in I find completely worthless. Meanwhile there is stuff I actively buy that I think is a great price in which others are happy to dump off to me.
Has a lot to do with experience but also the league everyone is in. Contacts and networking play a big role in how much a domain sells for. If you follow some of the domain bloggers they have a lot of name that are good that they can make great.
Which leads to another thing, I appraise a lot of domains on potential. Sometimes I do not, but often when I give a quick appraisal it is with everything considered. I take into account the market for it, development, trends, current backlinks, etc.