Neither of those reports found the piping material to be an issue and needing replacement. 

Plan on 5k for materials on a used 80s with soft floors and wall paneling.

Detailed blueprints, cost breakdown and material specs.

Do you all have any references for educational material on how to negotiate liens?

If both are materially participated activities, you will be able to net those activities at your individual level.

It's all awesome and actionable material. 

Newbie in NC, how is the best way to know the cost of materials when using the flip calculator.

Get a couple more quotes, plus compare material prices with some suppliers in the area  It’s hard to determine whether the price is fair because the nature of the project and the sizes are unknown.

Below is the language in the contractSeller's Failure to Comply or Breach: If Seller fails to materially comply with any of Seller's obligations under this Paragraph8 or Seller materially breaches this Contract, and Buyer elects to terminate this Contract as a result of such failure or breach, then the Earnest Money Deposit and the Due Diligence Fee shall be refunded to Buyer and Seller shall reimburse to Buyer the reasonablecosts actually incurred by Buyer in connection with Buyer's Due Diligence without affecting any other remedies.

Even then, I require a written agreement that explains exactly what work is authorized, what materials they will use, who will pay for it, when it will be complete, and what happens with the improvement when the tenant leaves.