Sellers and Buyers will enter into a contract subject to third party approval. The "third party" is the sellers' lender (holder of the sellers' mortgage). The sellers' lender must approve the contract (specifically, the sales price & other terms). That lender's review of the contract can take up to 3 or 4 months.
If you are not already working with a realtor, I would be happy to assist you with your home search and answer other questions you may have. Please give me a call !