1. 4 worth-vlaues: 5RMB, 10RMB, 20RMB, 50RMB.
2. Onlyvalid for 30 days, starting when it is obtained.
3. Onedelivery request can only use one coupon.
4. Coupons can be used to offset service fee.
5. If service fee less thancoupon value, remaining coupon value can not be refunded
