There is no one unified way to do it, probably, but the same way, I'm finally not sure to understand what you mean by illiquid.The same way, what is the meaning of a price not reflecting a market deal ? (That's a pure opinion of PM)."corp bond is so unique and less trade in the market" In this case, the only reliable option has nothing to do with quant analysis. It is all about evaluating the company value, thus the debt value, if it's not rated, find equivalent company, with correlation sources, and determine your target ASW for the bond. (A basket of reference bond)If you have a Private Equity business in your company, you should get in touch with them. They are doing this everyday.