FWIW Dept.
I think that a good ring is a fine indicator of a tight solder joint between rib and barrel. Not an absolute but better than any other "test" that I know.
One thing you can do to be a little more certain. Take a very thin shim or a long straight pin and run along the joint. If you snag, look at the place with a strong glass. If there is a space, take note and continue looking for more possibles solder gaps.
I have bought guns that did not ring, but there was an incentive. They were high grade guns that were in great condition otherwise. A good pair of tubes can be satisfactorily rejoined for about $250/$350.The added cost of blueing has to be counted, as well. If the gun is worth an additional $500/$700, then it is a good buy, ring or not. The seller might just be reasonable or afraid of holding onto a white elephant. If the barrels be of that dangerous Damascus, he may kiss you for being a money foolish nimrod.LOL
Best,
John
