Keep Track of Costs
Whatever you choose to sell, when buying (or making) merchandise, keep track of all your costs. Your "cost of goods" is not simply the item price you pay for goods, it's the total cost of acquiring the goods including shipping, traveling, hotel (if you're attending regional trade shows), and related costs. You can't determine your business profits unless you realistically determine the cost of acquiring your items. The same is true for handmade items. You'll never know your profit margins unless you track the cost of yarn for that handmade crocheted scarf.