I don't know anything about art appraisers, but considering the various auction houses that handle the stuff, I am fairly sure that there are some out there who do a good job and who understand what the stuff is really worth.
However, the actul value of art has to be determined not by any intrinsic" value it may be deemed to have (by either the artist or his critics, official or otherwise), but by what the market will bear, just like anything else, from Google stocks on down. That's the way it should be taxed, to the extent that anything should be taxed, which is not much, IMO.
Meant to ping you to #19.
Art should be valued according to the market, IMHO, like everything else, whether it be an internet stocks or an athlete's salary.
I'm familiar with some situations in which artists have tried to donate art to some museum or other entity and have been told that they'd have to get the work catalogued and formally appraised. If the artist has no track record of earning $25,000 for a painting, he can't claim a $25,000 deduction for contributing one of his paintings to a museum. In many cases the museum will turn down the donation unless the artist is a person of tremendous prominence. Most of them have a lot more art than they can display and there are millions of deluded idiots churning out millions of pieces of graphic garbage they consider "art", so the standard is pretty high.