I would go so far as to suggest that if the inspections from Fly-By-Night-Inspectors are known to be unreliable that the appraiser is getting into a situation were they would be unable to claim they had a reasonable basis to believe the accuracy of the facts asserted in those inspections.
The appraiser isn't responsible for the accuracy of those inspection reports (obviously), but they ARE responsible for the choices they make as to which inspections they believe to be accurate vs which they don't. "I had reason to believe this inspection report was accurate", so I used it; vs "I didn't believe the accuracy of that inspection report so that's why I declined to use it".
If the appraisers can't use an inspection company's inspection reports then that renders that company's reports unmarketable for the purposes of use in an appraisal assignment. If appraisers continue to use data they know to be error prone then that's on them. Moreover, those decisions undermines the legitimacy of their complaints about those types of assignments.