@Ken,
That's not the point though, it it? If you had sent him the correct bag in the first place, this thread would not exist.
Personally, I would have accepted your original offer, but that's not the point either, is it?
I know the rep business is unique and has it's own set of seller/buyer relationships, but in the end the responsibility lies with the person who made the original mistake. As the seller, you can choose whatever stance you deem appropriate for your business. But then you also have to live with the consequences of possible bad reviews. No matter how many forum members come to your defense, those bad reviews will still be sitting out there.
As part of my job, the shipping department reports to me, so I have a decent level of shipping experience and knowledge. I don't think it would ever have crossed my mind to package the bag to prevent humidity from ever reaching it. It's something I have no experience with. To expect the customer to do so, without explicit instruction, is unreasonable, in my opinion.
I'm not intending to be jabbing at you, but just trying to make the point that this one bag and subsequent bad review could end up costing you more than this single sale. Is it worth the risk? Only you can decide that.......