First private utility park- utility due diligence best practices?

Greetings Forum- we’re in 30-day due diligence phase on a 50 lot park with private utilities (septic & well- which will be a first for us). Outside of doing extensive utility vetting, if anyone has due diligence best practices on private utilities that he or she can share that would be appreciated.

We’ll be paying for a professional assessment for both the well and septic. One thing I’ve heard is the importance of a second assessment beyond the current utility service provider since the existing contractor could be in cahoots with the seller.

Thx!