Short sales are difficult at best to get to close. The bank doesn't have to accept your offer. The way the process works is once your offer is submitted the bank orders an appraisal or BPO. The bank then decides o if they are going to counter or accept. The listing price and the seller acceptance doesn't matter to the bank. The bank only cares about the net and won't accept an offer unless they get the required net. The net is based upon the as is appraised value and after all the expenses are paid.
You must have patience to close. It usually takes a minimum of 3 months to close and in the end you
could end up with nothing.
Also the home must appraise out for what you have offered or you would have to bring that extra money to closing or you would have to walk away.