Personally, when I order stuff online and look at reviews, it's common to say the odd bit of late delivery, or sometimes bad customer service. But selling keys that were obtained through CC fraud is simply unacceptable for any store in my opinion, add to that the bad customer service of outright saying that the customer is not telling the truth just to try and get a free key and a refund is just not on.
Sure, the person may not have known that the place he got the keys from were from CC fraud, but if he wants to run a legit company he has to verify the source of his products. No physical retail store would get away with selling stolen goods and just saying 'I didn't know the supplier was a thief'. Even if the keys were legit, they were all US CD keys, but not advertised as such, so wouldn't be that great for most EU customers.
Is the store legit? it's probably trying to be, but the store is either incompetent and clueless when it comes to obtaining cd keys from suppliers, or it is knowingly selling stolen goods. Neither of which sound like a company I want to do business with, and I would steer people clear of them.
I think selling CD keys like this should be a valid method of purchasing games, and more companies should offer this, I just don't think this is the right company for that.