Selling the entire lot and getting a good deal are likely mutually exclusive outcomes. Your use of the phrase "expected percentage loss" leads me to believe that your expectations are too high. With all due respect, you have not provided enough detail for anybody to assist beyond the general recommendations already provided. Can you identify one or two of the "rare" coins and run us through the exact process you used to determine your value estimates? As far as negotiating tips, be prepared to decline all offers, be willing to spend an extraordinary amount of time to maximize your selling price and take into account the buyers motives. Remember, your out of pocket cost for these items is zero.