I assume this is the auction?
First of all C&H made quality guns.
Could be great or could be a money pit. Paradox guns can be a lot of fun and still quite useful in the field. In Namibia I once rolled to warthog for leopard bait and made a small mountain of sandgrouse one afternoon at the same waterhole, If you use the search function, there has been a good bit of discussion about them here over the years.
That stock is a mess - that said, on a penny auction if you can get it for a song then it might be worth a quality restocking effort.
If I remember correctly, the Avant Tout version of the A&D boxlock used a barrel mounted ejector system which could cause issues over time. Judging by the buggered screws, this one has had those issues,
The rifling looks intact which is a big deal on these - it was often bored out once paradox ammunition became rare to non-existent.
I would want to know from the seller if it is still on face - ask him to remove the forend, shake the gun and see if there is any detectable movement.
Is the solder still sound holding the barrels together? Ask him to suspend them by the forend hook and tap with a wood mallet. They should ring not clunk.
Finally, getting one of these shooting requires a lot of commitment to ammo development. You might get lucky and find some of the recent production H&H paradox ammo and discover it regulates reasonably. My William Evans shoots it accurately to 50 yards and a bit. On the other hand, it shoots the loads developed by Ross Seyfried sub three-inches at 100 yards.