Can we ever evaluate technical debt?

Every couple of months, I talk to an entrepreneur who is interested in building a marketplace for buying and selling app businesses (i.e. the actual IP and ownership of an app or other piece of software). These markets always seem to suffer from a lack of liquidity, and one reason why is that it’s really hard to know how much technical debt is latent in a codebase.
First, the developer behind the codebase may not even be aware of the technical debt they have piled on. Second, until a softw