1)Shipper can't pay duty. Receiver must do customs declaration and pay duty if the value is over the duty-free standard.

2)In case of return for refund, many bad sellers intensionally avoid making customs clearance so that they can tell buyer that they can not get the return and therefore refuse to issue refund. You can consider this as a game of fraud.

If point 2) matches your case, you need report fraud to your marketplace (Amazon, ebay,aliexpress, paypal etc). Tell the marketplace that the seller doesn't make customs clearance and avoid to accept return and issue refund. If other buyer filed similar cases against same seller, you will get refund.

First, every receiver must tell shipper to print receiver's mobile phone number in the parcel. Once the parcel arrives in China, China Post will send a secret code in mobile text message. Receiver can download an APP to make online customs clearance with that code. Also receiver can make duty payment through that APP.

If receiver's correct mobile phone is not printed in the parcel, the procedure will become quite difficult. receiver needs to contact China Post in person and go to the local China Post head office to make customs clearance. Normally it is quite difficult to do this.

Remember, China does not have an accurate address system like Western countries. Receiver's CORRECT Mobile phone number is much much much more important than receiver's correct address which, in many cases, does not exist.

if the receiver does not make customs clearance and free storage time expires(different china post warehouse has different free storage policy), the parcel will be returned to original shipper's country. You can keep track the parcel in usps.com, once the parcel is returned, USPS.com will show new update.