The following trick only works between the two indicated vendors. You can usually buy items back from Expat at half the price you sold them to Dr. Michel for. First, successfully complete the side quest involving Dr. Michel (from the Med Clinic) and her blackmailer. After the quest is complete, you will get a discount from all the goods she sells. Start selling her all of your expensive equipment. Then, travel to the Wards Markets, and talk to the merchant named Expat. You can buy all of your items back for cheaper than you sold them for. Return to Dr. Michel, and sell her all of your items again. Repeat this process as many times as desired.