Sounds like they didn't hire one in the first place - {or perhaps a home inspector who got his 'training' by signing up with one of those job training programs "As Seen on TV"!)

I'm wondering if the pot growers where renters - and then the home owner performed the cover-up work with the special primer.  If so, aren't there clauses that places the responsibility to fix things back on the sellers - for not disclosing problems?