Negotiation advice needed - Urgent! Property under contract!

[David Kuhlke]

Hello BP community, 

Need some advice on a property I have under contract. I discovered during the due diligence that here are 2 breaks in the sewer line. The cost is $7,500 to fix. However, the seller claims there is nothing wrong with the sewer line despite my agent sending them the sewer scope video evidence along with an official quote. The seller claims they talked to another sewer contractor that said the cost would only be $4,000 if it had to be fixed. I was able to get in touch with the contractor the seller spoke with. The contractor is planning to go out to the property to do an assessment in person. When the seller found out about this, they dropped the price by $1,500 and said I have 24 hours to respond no matter what the contractor finds. If I don’t respond within 24 hours they are going to send me a mutual release agreement. I’m surprised by the seller’s behavior. What can I do in this situation? What should I do? 

Thanks, 

David