Someone "cleaned up" the checkering very amateurishly. I wonder what else was done to this stock?

BUT, the real problem is that the gun was shipped assembled AND completely unprotected against bending forces.

The seller chose the shipper, not you. The packing was done incompetently. It is NOT your fault, nor do I think should be your responsibility, unless you agreed to terms giving you the risk of shipping.

You may want to ask for a return and refund, particularly if you had no reasonable way to know about the buggered checkering.

Fred