Due Diligence upon closing the purchase

I am ready to offer on a park in Ohio. The seller has had to replace the sewer treatment plant. Good news that if I purchase I get a brand new treatment plant, but what are the pitfalls and watchful steps to make sure the purchase goes smooth as the treatment plant will be repaired …chances are, after the purchase. Not a lawyer but I am thinking holding back some of the funds? …any help or strategy would be greatly appreciated.