Service guarantee is a dilemma for e-sellers. As it will increase buyers’ purchase intentions, but it may leads to more return goods too. Our research makes an effort to study the influence mechanism of service guarantee, in order to help e-seller to make their retail decisions. The results of our empirical analysis indicate that the higher the strength of service guarantee is, the higher degree of the sales level is. Besides, service guarantee will influence the refund rate with inverse U-relationship. So it is necessary to select a reasonable level of service guarantee.