This is an interesting concept of the sunk-cost fallacy.
Contemporary Cognitive Therapy: Theory, Research, and Practice - Google Books
Applying this concept to boat buying may lead one to follow a purchasing process that is a little different from normal.
For example. Lets say you just had your potential boat surveyed and it was noted that the keel boats for a flanged iron keel had not been checked in 25 years.
If you were to buy the boat one of the first things you might do it to extract a couple bolts to check or replace them.
So typically someone would buy the boat do the work and have to just suck it up if the bolts had to be replaced.
What if you were to pay to have a couple bolts inspected before purchase.
The survey is already a sunk cost. If pay maybe $500 extra to check the bolts and they are bad then you still don't have a boat but maybe you can get some money from the PO or if you can't make a deal you are at least not committed to an expensive repair.
So my question is has anyone as part of the purchasing process gone beyond the standard survey and with the owners permission had other work done on the boat before purchase or talked the owner into doing exploratory work.