Seller wants to back out of contract

[Tracy Kirby]

We have been under contract since 4/30 and doing a 203 k loan which requires more paperwork and takes a little longer. We are ready to close and have already come back from underwriting and just waiting on appraisal. The seller refused to allow the appraisal and wants to back out of the contract to sell us the house. How long does it take to take legal steps against this seller? Is it normally 100% the buyer will get awared to purchase the house? We dont want to put money up to go through legal steps if it will end up in same resolution of not getting the house. 

Thanks