If a motion is filed, the court will review the appraisals and other evidence submitted by the parties and attempt to determine the market value of the property. A professional appraisal holds a lot more weight than Zillow or an estimate made by looking at some comps in the area; but it costs money.
Were your mother to file a properly supported motion, the trustee will presumably respond with more to support his claimed value than "Because I say so" -- if he doesn't, the court is not likely to give his position much (if any) weight.Quoting needsomehelp

