I take issue with "any retail store." That's really not true these days for practically any major retailer when we're talking about standard goods.
You go into Target and you buy a toaster from them on the last day of their Toaster Sale. You take it home and lets say you literally get shocked by it - the toaster does not work as it normally should. You then bring back that toaster to Target and request a replacement. But the toaster is now twice the price. But guess what? It doesn't matter. They give you the replacement from their current inventory to make you whole for your prior purchase. Only if it's completely out of stock would you get the refund instead. You don't pay the difference for the new toaster, because it wasn't your fault the first one was messed up. Target doesn't have to offer you the replacement toaster though. They could say "Here's your money back, good day." and leave it at that. But if Target wants to remain in business, they better have a replacement policy.
That's really the issue here. The store is supposed to make you whole on your original purchase for their mistake. So they can either refund your money, or send you a replacement at no extra cost. Either one accomplishes that. Saying "Yeah we'll replace it if you pay $20 more even though it was our fault" probably rarely happens and I can't imagine any store would think that's good business sense. That might even violate the agreements they have with credit card processors. Sure refunding the money then expecting the customer to place a new order at a higher price is a round about way of hoping for that same result, but at least the customer has the freedom to take their money and give it to another retailer instead.
As long as CGN refunds the money, then fine, it was a fair end to the business transaction, even if it ultimately isn't great customer service.
I once bought a TPB from IST that had a manufacturing defect. When I noticed it, I emailed them and they sent me a new copy out right away without requiring me to send back the bad copy, no further questions asked. That's great customer service. They could have forced me to send it back on my dime, then refunded me the cost of the book, then told me to take a hike. But they didn't because they're a great company and realize how to build a business and a reputation.
Personally though, I don't think CGN gives a damn. They might not have great customer service when issues arise, but they're doing something to stay in business. Their brick and mortar store has expanded to two locations. They snagged one of the best domain names for the online front. They do actually offer low prices on a lot of things, though shipping and/or tax can offset that. But they're still a classic local comic shop when they jack up prices above cover because something has become "rare." Probably the vast majority of their transactions go just fine. But the ones that don't seem to reveal their true nature. And you can go read their Yelp reviews for Pulp Fiction Comics in Long Beach, CA and see that some of their customers get the same nasty treatment in-person. But in the end they still have a 4 star rating and plenty of satisfied customers. So there really isn't an impetus for them to change anything at this point in time, because those of us having this conversation here are absolutely in the insignificant minority for the moment.