The paper forthcoming at JFE:
http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2442314
The paper that existed at least since 2011 (probably got rejected everywhere):
http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1923793
(2011 version is here: https://www.researchgate.net/profile/Ningzhong_Li/publication/228149730_Customer_Relationship_and_Debt_Contracting/links/00b49522d3c4090021000000.pdf)