Recent surveys by the National Association of Realtors found that about one in three Realtors have experienced contract problems related to home appraisals during the last three months.The surveys showed 15 percent of Realtors had a contract renegotiated to a lower sales price as a result of a low valuation, while 11 percent said they had a contract cancelled because a home's appraised value came in below the negotiated price. Another 9 percent reported that a contract was delayed by a low valuation.Good news about improving housing markets had made the appraiser's job even more difficult. The S&P/Case-Shiller Home Price Indices posted a fifth consecutive month of gains in August, with a 20-city composite index showing home prices up 2 percent from a year ago.Lenders want to see compar...