The seller offered a full refund or they will pay for repairs…any thoughts?
Good. Take them up on their offer. More than likely it was broke because of the the way it was packed. Was the box heavily damaged? If not, the person that packed the rifle was at fault.
I can only tell so much from pictures, but that would not be an easy break to repair.
I had a rifle that the toe was broken during shipment because the shipper didn't fully secure it in the box. I had Jack Brooks repair it which cost $200. The seller paid for it plus discounted the final price of the rifle, i.e. gave me a small refund. A professional like Broods would probably charge a lot more than $200 to repair that break.
Unless you have access to a professional muzzleloader gun restorer, probably best to return the rifle to the seller and get a full refund.
You mentioned the hammer was loose. It shouldn't be. It could probably be fixed, but just one more reason to return the rifle for refund.
I've purchase a number of longarms from several big name auction companies. They know how to pack and ship to minimize potential damage during shipment.
Here are some examples.
In this case, there was three layers of cardboard--a box in a box in a box. At a minimum, it should be two layers of cardboard--a box in a box. For real expensive long guns, a wood crate or aluminum case is best.
The guns are wrapped in bubble-pack with extra wraps at the muzzle, around the forearm, around the lock, and at the butt.
They are placed in the inner box with a generous amount of foam peanuts that ensure that the rifle cannot move in any direction inside the box.
Due to the weight of the barrel, if the rifle can move around in the box the stock is subject to being broken in the lock and/or wrist area.