Once upon a time, an eminently sensible earth pony named Clyde wanted to establish a rock farm, but lacked the lands and the funds to do so.
One day, he found a rich pony named Smart Cookie, who was looking for a pony like him.
"We can do business together," Smart Cookie said. "I have a good, solid plot; perfect for a rock farm. I can lend it to you for a season, and give you the funds you need, as long as you give me half of the rocks you harvest."
"Very well," Clyde said. "Which half of the rocks will you want? Divided by weight, size, sedimentary and meta-"
"To be frank with you, I don't know anything about rocks. That's why I am looking for a sensible pony to farm my lands. Just give me the rocks above the ground, and you can keep the rocks under it. That way, I can know with just a glance how my part of the rocks are going."
"Good enough for me," Clyde said. And they wrote and signed two copies of the contract as sensible ponies often did.
Clyde worked, toiled and moiled, and when the time of the harvest came, he had ensured that the rocks above the ground and the rocks under the ground were worth about the same, so everypony was happy with the division.
Because of that, Smart Cookie kept leasing his lands and his funds to Clyde, and they became steadfast friends.
Moral: Cheating might lead to quick riches, but fair dealings lead to repeat customers. And if you can afford to trust someone, it can very well be worth your while.