My gut feeling is it's going to cost around $4,000 to repair and has been there for ages.

Feel free to reach out! 

BUT I have also heard that it could trigger a due on sales clause, bringing the note fully due at any moment.

while I totally understand the frustration especially purchasing what was supposed to be a new and ready to go asset, but these things are pretty common so don't feel to discouraged. 

Buying site unseen is a huge risk unless the buyer and wholesaler have a history doing deals together.My buyers trust the deals that I bring them, but I also provide them with in-depth inspection reports along with photos/videos of the inspection along with multiple cost to completes through multiple contractors.

You're certainly correct, this market it pretty awesome, which brings in a lot of competition. 

I wasn’t feeling good about anyone pursuing me to lend me money, but this cements even more why to stick with regular lenders when possible. 

This gives you a foundation for making a fair offer.Secure Financing: Be prepared to show you’re a serious buyer with funding lined up, whether through cash, traditional financing, or a creative option like seller financing.Have a Strategy for Repairs or Development: If the property is distressed, outline how you’ll handle improvements to bring it back to productive use.

Are they bringing equity?

LTV & CreditEliminate the emotion and treat this like the business it is.In my opinion it does not matter who the borrower is as long as they have a track record of ATR (Credit)And I feel comfortable with the leverage (LTV)