From the New York Times story "Suddenly, Stricter Appraisals" by Lisa Prevost

Mortgage lenders determined to stave off additional losses are demanding more thorough home appraisals and carefully reviewing valuation figures. If an appraisal is deemed too thin on supporting data, lenders may reduce the loan amount for the property, or not make the loan at all.

And there is little room for arguing with banks about a valuation.

“The banks are much less willing to make any exceptions at all,” said Bob Grace, a broker with Anchor Mortgage, in Westport. “They are looking for ways to squash a deal, as opposed to finding a way to make it work.” Mr. Hastings recalled one lender who walked away from a deal involving a “really strange contemporary” because the company wasn’t convinced there were any properties that compared with it for valuation purposes.

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