You're not getting much love in the thread, which is why I didn't reply earlier, but the bolded bothers me. It doesn't matter how much you're incurring the business. It doesn't matter if it's $2.51 or $251, scale is irrelevant. A customer mistake is his own mistake. Sellers are under no ethical obligation to ameliorate customer fault with grace. I'd think that, in a sometimes confusing web environment, most mistakes are actual mistakes and not intentional, so it is often beneficial for the seller to further the relationship with the buyer by extending grace. But again, that is not the seller's obligation.