What is the criterion of morality according to Buddhism?
In the admonition given by the Buddha to young Rahula, there is the answer.
If there is a deed, Rahula, you wish to do, reflect thus: Is this deed conducive to my harm, or to others' harm, or to that of both? Then is this a bad deed entailing suffering. From such a deed, you must desist.
If there is a deed you wish to do, reflect thus: Is this deed not conducive to my harm, nor to others' harm, nor to that of both? Then is this a good deed entailing happiness. Such a deed you must do again and again.
Thus, in assessing morality, a Buddhist takes into consideration of the interests of both himself and others - animals not excluded. Good deeds are essential for one's emancipation, but when once the ultimate goal of holy life or enlightenment is attained, one transcends both good and evil. Morality is a means to an end, but not an end in itself.
[http://web.singnet.com.sg/~alankhoo/Precepts.htm]
THE FIVE BUDDHIST PRECEPTS
1. Do not Kill
One must not deliberately kill any living creatures, either by committing the act oneself, instructing others to kill, or approving of or participating in act of killing. It is a respect to others' lives. One should not deprive others (animals not excluded) of the right to live. If one is hurt or killed, one's family, relatives, friends will suffer. It is the cause of rebirth in Three Evil Paths. The effects of killing to the performer are brevity of life, ill health, handicapped and fear. In observing the first precept, one tries to protect life whenever possible. Furthermore, one cultivates the attitude of loving kindness to all beings by wishing that they may be happy and free from harm.
2. Do not Steal
It is a respect to other's properties and the right to own property. If something is not given, one may not take it away by stealing, by force or by fraud. Besides these, one should avoid misusing money or property belonging to the public or other persons. In a broader sense, the second precept also means that one should not evade one’s responsibilities. If an employee is lazy and neglects the duties or tasks assigned to him, he is, in a way, "stealing" time that should have been spent on his work.
In its broadest sense, observing the second precept also means that one cultivates the virtue of generosity. A Buddhist gives to the poor and the sick because of their need. He makes offerings to the monks, nuns and masters because he respects the qualities they possess. He is generous in his gifts to his parents, teachers and friends because of the advice, guidance and kindness they have shown him.
In addition, Buddhists should also offer sympathy and encouragement to those who are hurt or discouraged. It is said, however, that the best of all gifts is the gift of the Dharma in the form of teaching it or in the production and distribution of Buddhist books.
Greed is one of the Three Poisons, which leads us to attachment and suffering. The bad effects of stealing are poverty, misery, disappointment, etc.