Most lenders will NOT accept a short sale, unless the borrower is delinquent.
If the seller (s) are only one payment behind they may be able to speak to customer service or the collection department for a work out solution.
In this declining market some lenders are considering a short sale even if the borrower is current with their payments. If the borrower can demonstrate a true hardship and show the inability to make future payments, some lenders are open to negotiation.