There isn't a threshold that I am aware of. Way back when the regulators required an "acqusition appraisal" on all real property collateral, there was no threshold. There are regs about not having overvalued assets on your books. The only way to prove you don't is to get an appraisal. How else can you establish the price you are going to bid in at foreclosure also ? It seems you could put the bank at risk for litigation if you don't have an independent valuation.
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Societies that do not find work in and of itself "pleasing to God and requisite to Man," tend to be highly corrupt.