Is chaining a dog in the backyard cruel?

Our dog has antagonized the obnoxious people next door for months. They are fed up and so are we, because she jumps the fence and we cannot keep her in the kennel very long (trainers directions). If they are so cruel, why do pet stores sell them? If she is in her own backyard on the extra long chain that she can get to her food and water to, can someone legally come in the backyard and holler cruelty?