Hello and thank you for the opportunity to assist you. My name is ***** ***** I will do my very best to answer your legal questions.
I'm sorry to say that I think that you'd have a hard time convincing a judge that the appraiser, who was likely only paid a few hundred dollars for the appraisal, should be forced to pay $75,000 due to his mistake. The appraiser had nothing to do with the interest rates.
Look at it like this: If the interest rates went down instead of up, do you think the appraiser would have a good case against you for $75,000 since he saved you money? After all, he could argue that if it weren't for his mistake, you'd have closed on the deal sooner and paid more interest, and that he should be rewarded for it and share in the money. I think you know that argument would be absurd. Logically, however, it's no different than demanding $75,000 from him in the situation you're currently in.
Also, more than likely, the terms of hiring the appraiser include something indicating that you agree that he is not responsible for any losses as a result of his appraisal. I would be very surprised if he didn't have some sort of waiver like that.
I'm really sorry for the bad news, but does that answer your question? Please let me know if you need clarification, and please remember to provide positive feedback. Thank you!