I don't think the fault is entirely with EoM. As you pointed out, you returned the shoes due to bad QC on G&G's part. Yes, EoM should have checked the shoes prior to dispatching them to you. But then I have also received faulty G&Gs from another vendor. The important thing is how the vendor handles the issue - eg offer a full refund or get G&G to make you another pair.
May I know the reason? Since the shoes are likely to be of different sizes anyway, different sized lasts would need to be used. I can't see why having the same width would lead to production efficiency and hence elimintae the upcharge.