It is unethical to accept sexual favors for rent.
One of Carl's tenants offers to sleep with him in exchange for a free month of rent, since she is short on funds.
Carl wants to help his tenant.
Carl turns down the proposition, but still reassures his tenant that she can pay the rent late.
Carl accepts the sexual proposition and sleeps with his tenant.
Carl's tenant feels relieved that she doesn't have to worry about rent or compromise her morals.
Carl's tenant feels like she has violated her moral code.