There are probably a lot of people who believe that appraisers have a certain amount of legitimate discretion as to where an appraised value can come in, but that’s really not the case. An appraisal is supposed to call it straight down the middle, not favoring one side or the other. An appraisal that does otherwise is substandard and should be considered by all to be intolerable.
What appraisers can do is to play the odds as to what a lender will accept. When times are good and the lenders don’t care, the appraisers can abuse the lax level of oversight and review and submit overvalued appraisals. When the lenders look more closely then even the most crooked appraisers have to clean their acts up.