Now I understand why four days is so long. They must be hard to reach but that is odd due to the market. Perhaps the price bothered them? I would call your realtor and ask her to push harder for an answer.
Are the sellers available? Is it a bank owned property? A bid for a HUD? Did you put a time is of the essence date for an answer from the sellers? Most of the time it takes one day or less with a regular sale. Bank owned .... no one knows... it's up to the bank. HUD, bids are opened daily or weekly.