Most short sale listings are priced at lower than current market value to attact more interest from buyers.
There can be a mutual acceptance on a price, but all terms, price and conditions are still subject to the short sale lenders' approval.
It is best to submit a price close to the current real estate market value because the short sale lenders will have their own appraisal. Submitting a reasonably priced offer is the best thing to do. There is a better chance the short sale lenders will accept the terms/price of current offer.