It's wrong for people to defraud others.
Tim promised his roommate he'd have enough money to pay the rent that month, so he decides to sell his old, broken motorcycle.
Tim wants to earn enough money to pay his rent.
Tim asks his roommate to help him fix the motorcycle, so he can sell it.
Tim places an ad on craigslist, listing his bike as being in top condition.
They get the motorcycle working and Tim sells it for more than enough money to pay the rent.
Tim can't pay the rent when no one buys the motorcycle because they find out it doesn't run.