As has been said before, clean it good and shoot before you sell it.
Here's my story on that subject:
Years ago, my wife's uncle sold me one of his benchrest guns. This is a custom rifle, built on a Sako single shot long action, 30" Hart barrel, 1-14 twist. It's in a McMillan stock, with a Canjar single-set trigger, chambered in .220 Swift.
I shot it a bit--wasn't too happy with the results. I could not get it to shoot a group of less than one inch at even 50 yards. I was disappointed. Inspection of the rifle showed black and dirty for the first two inches of rifling. So, I thought the same as the OP--I was going to send the rifle to Hart, have them cut to a 26" finished length and recrown the barrel.
Then my wife got an Outer's Foul-Out for me.
Operation is simple--clamp the rifle upright and place a steel rod (very skinny) down the bore. It has washers on it to center it. Now, plug the chamber and fill the bore with solution. Slide the control unit onto the rod, and put a metal clamp that is wired to the control unit on another metal part of the rifle.
It is a reverse electroplater--it attracts deposits from the walls of the bore to the rod.
I let it run for a full hour. I then disconnected it, and poured out the solution--it looked clear. I sighed, and then started a jag with patch to dry it out.
The jag went in--and stopped cold. I was confused--I had used the same rod and jag combination many times. Thus, I decided to give the rod a couple of taps to help it along. After two taps with a rubber hammer, I heard a loud "CRACK", and then the jag moved freely.
Out came a solid SLEEVE of rock hard carbon, liberally shot through with copper streaks!
The next time I took it to the range, it shot a 5 round group of less than 1/2 inch, from the bench at 100 yards.
So, give it a good cleaning first. If you can, take a Foul Out to it.
And if you want to re-barrel it, send the whole action to Douglas, and spec a 4X Premium barrel, in the caliber you want.