Where can I compare whether an OTC bond's price is reasonable?

At the Korea Financial Investment Association's Bond Information Service (kofiabond.or.kr), you can check mark-to-market benchmark yields by credit rating and remaining maturity and compare the yield with bonds of the same profile.

Prices of exchange-traded bonds can be viewed on securities firms' MTS and HTS (mobile and home trading systems) or on the Korea Exchange's information data system. Prospectuses and credit rating reports are available on the Korea Securities Depository's SEIBRO and the Financial Supervisory Service's electronic disclosure system (DART).