The first thing to do is go look. It may not be what he says it is.
The Cop's told me that probably the people who stole my 20 Hp had it advertised as as a "Big Outboard motor" with a problem, for a very small amount of money. Hoping some Rube might think he's skinning a Dilbert and getting a deal on a better-than-advertised motor.
Second, a motor that old, and not running is only a parts hulk.
If you are one of those Hapless but talented do-it-yourselfers, go ahead and make an offer.
If you dont know what your getting into, and think you might need this motor in a hurry, dont take the chance. Buy something that's working.