I don't think there's a straightforward answer to this.
I'd guess the best grade of any model would be the one to go for, but the most important issue would be mechanical condition. Good wall thickness,
tight action, good working locks , ejectors and, well, plenty of life left an all of the above. It could make or break a good deal.
The smallest of jobs on a high end gun could seriously eat into your profit margin very quickly.
It's not all bad news tho, as was already said. The gun may well hold it's value rather than depreciate. Certainly not a bad thing, especially if you've had years of fun shooting the thing in the meantime.
Dealers. A good dealer should have inspected the gun before you buy it and give some kind of warranty with it. Buying private is far more risky. I think the people in the know will spot any problems/defects and use them as a bargaining chip or just simply walk away.
If it was straightforward, we'd all be doing it.
I don't mean to sound pessimistic as there are gems out there, and what better pleasure than being able to take one out and use it.
I wish you good luck in your search.
