Professor William Black:

Basically, they extorted appraisers. When I say "they", I mean the lenders. If you were not willing to inflate the appraisal, they blacklisted you and you could not get a job. No honest banker would ever inflate an appraisal. That is an example of a Gresham's dynamic. As I say, Swift actually identifies this with the Lilliputians in 1726.