Lis pendens does not stop anyone from selling. A seller can sell up to the last minute before foreclosure. In fact I have experienced sales hours before the house was scheduled to be sold at the court house steps.
South Florida is becoming the short sale fraud capital of the universe, so you need to be EXTREMELY careful about who you choose to represent you. You need to find a Realtor familiar with the short sale process and preferablly one who does NOT do the negotiation themselves, instead using a third-party company with the expertise to negotiate. You should incur NO COST for the short sale, although you should engage an attorney to answer the foreclosure suit to avoid summary judgement.