Hi Bill, My experience with diesels is that its not as important how many hours its been run as how it has been treated. Don't change the oil and run it at low power for 500 hours will be harder on it than love and attention for 5000 hours. 2300 hours with proper care and attention is peanuts on a diesel. A good mechanic can tell fairly accurately by looking and listening. Oil analysis is a good indicator too as long as its not fresh oil.
Maintenance records are good.
Pull the injectors and they will tell a tale to the experienced eye. General cleanliness is a nice indicator too. High hours alone is no reason to reject. Low hours are no reason to accept. Do the assessment or pay to have it done.