Hi,
When someone tackles a project on their own, they are saving lots of money, but are also taking on some risk. If a person has an alternator installed at the dealer and it fails in a month they will have it replaced no charge. The dealer has to absorb the cost of the labor and such, but they factor callbacks into their prices. If you bought an alternator at the local auto store, would they pay for labor and such and car rental for downtime? Most likely not.
Virtually everyone here on GJ does their own work because they enjoy it and they save a bundle. It's very gratifying to see so many happy customers 99% of the time.
No manufacurer or supplier or home center gives money for labor and other expenses associated with a defective product. If Home Depot sells you a bad window that you installed, their only obligation is to give you a new window, and the labor and hassle is the customers problem. That's the risk in DIY projects.
We have had some minor issues over the years with products and we either give free product to correct it, or a refund. No one has complained or asked for more than that.
Justin is an excellent and reliable supplier, and by offering full refunds has more than fulfilled his obligation. Most likely he will get little back from his supplier, and has other soft costs like time and legal expenses. Expecting payment for anything beyond what was initially spent in our opinion isn't very fair.