Buying Art is not like buying Detergent; the key is to "buy intelligently". Art buyers often make the wrong decision when comparing two examples of the same Work of Art with the objective of "saving money". Many Buyers fall prey to buying the Work of Art with the lowest price, and often not the best.
Daniel Grant wrote a WSJ Article titled Why You Can't Always Trust Art Dealers which casts a negative light on Art Dealers. We don't condone the ethical behavior cited by Mr. Grant and agree due diligence is essential to protect financial harm.
However, condemning Art Dealers is similar to saying you cannot trust all lawyers. Due diligence by Art Sellers/Buyers is necessary. Seeking a second opinion from a knowledgeable/reputable Professional Art Dealer can help avoid financial disasters since novice Art Buyers/Sellers are at a disadvantage regarding Authenticity, Condition, Title, etc.
1. Ask questions.
2. Get references.
3. Do not accept hyperbole.
4. Avoid experts in everything.
It is doubtful that any Art Dealer is an authority in everything. And never sell your Art to the person who also appraises it since it is a conflict of interest. If you want an Appraisal, seek a legitimate Appraiser who has the scholarship and connoisseurship of the respective field they are appraising, but do not also sell them your property.
Qualified Appraisers will never appraise any type of property without a physical inspection. Any Company/Independent Appraiser who says otherwise is not doing you any favors, especially for accurate appraisals.
As Mr. Grant suggested, artnet.com, artprice.com, artvalue.com, etc., are useful tools, but only relying on these references is limiting. Buyers forget that when you compare prices, Condition Matters, and these Art research tools omit this key point.