Complex sentence: Even though she already hade a relation in the United States who often sent her goods to sell in her retailing business, they told her they were in the same business, that they were retailers and would sell her goods at cheaper price and she believed them.
Split into simpler sentences: Even though she already hade a relation in the United States who often sent her goods and these people told her they had the same goods and will sell at cheaper price. They told her they were in the same business, that they were retailers and would sell her goods at cheaper price and she believed them.