From Cubic Castles Wiki
Trading is one of the most popular practices in Cubic Castles. All you need to know is how to make cubits and gain profits.
Profit - money gained
To make sure you use the economy to your full advantage, you must be familiar with prices. If you're wondering about a block/clothing price, visit a friend or other shops. For those who wish to do option two, write down all the prices you see in different shops. After doing so, calculate the average price of the block/item. Make sure the prices you're putting into the formula are reasonable. Prices tend to fluctuate in Cubic Castles so be alert. All must remember that the higher quantity of an item, the less it's going to cost. That's why umbrellas cost so much. Trading is full of ups and downs but it is fun to do. Especially if you want to work in a business someday. Heck, you may end up as staff for Cubic Castles.