With the Bay Area real estate boom splitting into so many divergent microtrends -- some neighborhoods careening southward, others chugging along, with still others gaining speed despite all odds -- the necessity of an accurate appraisal has become more crucial than ever.Hired by lenders or mortgage brokers or sometimes attorneys, appraisers determine the value of a property by looking at recent sales of comparable properties, doing inspections and analyzing the larger market. Unlike agents, brokers and lenders, all of whom get paid on commission, appraisers are just about the only ones who have no vested interest in the deal going through. Instead, they get paid for their work by the job: usually between $100 and $500, but sometimes as much as $2,000 for a sprawling rural estate.