Here are some things to consider. The Seller may work out a loan modification with their Lender. They may do cash for keys. They may not agree with the terms of the Short Sale and decide to hold on to the property. The Lender may foreclose.
If you have a buyer agent, they should discuss the details of a short sale before you write an offer. Even better, before you look at short sales. You may decide that short sale homes are not for you. There are no guarantees, it can take a long time. They usually are as-is. It can be frustrating.
The contract is to protect you and the seller. Please have someone explain it to you.
The short answer to your question is, "YES. The Seller can cancel after they have accepted your Offer."
A short sale is a different kind of transaction than the normal real estate purchase. You are essentially going to wait while the Seller negotiates with their Lender(s) for approval to sell you the house at a price lower than what is owed to the Lender(s). This process can be lengthy, even stretching out to many months before you have a final answer.
You'll need two things during that time:
1. Patience. While you've submitted all your documents to your Lender for your mortgage approval, and you keep your documents current and updated, you'll grow frustrated with the lack of any communication from the Seller about the status of the short sale. This is common, both the poor communication and the Buyer's frustration. Prepare for it.
2. Maintain your credit scores. Be sure not to make any dramatic changes to your credit report that could affect your credit scores. Pay all bills on time. Don't CLOSE any accounts. Don't open any new accounts. Don't run up your outstanding balances to max your revolving debt.
Once the short sale is approved, you may find the price you offered is not acceptable to the Seller's Lender. They may come back and counter-offer your price, so you will have to reconsider at that time if you wish to pay more than your original offered price.
The three rules of real estate: Location, Location, Location.
The three rules of short sales: Patience, Patience, Patience.
I hope that helps!
If you haven't signed any paperwork yet (which would include the purchase contract/offer), then you haven't really made an offer because real estate transactions need to be in writing and all paperwork has to be signed by all parties. Also, with a short sale, the seller's lender(s) have to approve the short sale (in writing) for it to 'really' be 'accepted'. A seller cannot close a short sale without lender(s) approval. If the lender(s) doesn't approve the short sale, the deal is dead - even if the seller accepted a buyer's offer.
If both parties have not signed a purchase agreement, then there is no acceptance of an offer by either or both parties. Additionally with short sales the owners lender has to agree as a contingency of the sale or the sale is dead.