There was huge moisture issues under Johns crawl space. Most homeowners say i'm not spending money to repair moisture issues. What happens is, moisture will destroy your home and the longer you wait the stronger the chances are of rotting floor joists and beams, also the chances of mold and termite damage increase dramatically.
Whoever you hire just make sure there's a guarantee that your floors will never have a problem swelling, cupping, buckling or sagging. The moisture levels must be 12% or below before they are sealed with 2LB closed cell spray foam on all wooden members under the house.