If you choose to sell back Prospector items to the shop you will be refunded 80% of the golden nuggets. From the 'Boost per nugget' section, you can see that some pieces are more efficient than others. Therefore in order to get the most out of your nuggets, it is highly recommended you save up, and obtain each piece in the following order: 1st - Jacket, 2nd - Legs, 3rd - Helmet, 4th - Boots.