Determine the maximum amount allowed! Decide how much you can pay for the coveted case in advance. This will help you avoid a variety of vendor tricks and you will not return too much money for you not just the thing you need, just because its price is greatly downsized and it seems to you to be too advantageous to refuse the purchase. However, take into account that during the trading period, the seller should under no circumstances know the maximum amount you are willing to pay for the item. While some sources recommend that you set a maximum allowable price, you can pay more than it would be possible.