I don't think the OP should have gotten a refund. I also don't think that the GOG representative was rude.
However, regarding this thread... seriously, if the OP didn't leave because of his disappointment, he'll surely leave because of Weclock's and OutOfTimer's rudeness.
Despite what you might think, you're NOT helping GOG by being obnoxious. They're trying to attract more customers. In case you didn't notice, one of their advertised strengths is "classy community".
GOG, I think you need to moderate your forums.

I hate you guys. Now I have to check out Arx and probably put it on my polished game-shelf for immediate download.
*shake fist*
OP: Sh*t happens. I've done my fair share of "oh no, I didn't mean to click that" in my time. I write them off as added experience and go to the trainer and advance two more levels so I can wield that huge double-handed axe that I just found in the Temple of Moo. Err. Back to MM3.

You won't regret it. Even now that game still looks very, very nice and plays very smoothly. The magic system may take some getting used to but if you persevere it will become second nature.

I know this thread is dying down now, but I want to comment as a new customer Somebody made a comment that said " The guy is annoyed at what could very easily be taken as a flippant response (we just know better because we are part of the community) ".
I'm a new customer, I'm not familiar with anyone here, and I am honestly baffled as to how someone could get angry at the support teams response, even if you weren't chummy with them. There was no "snark" at all. The OP just struck me as overly sensitive who was going to complain no matter what since he didn't get his refund.
Some of the responses by posters here might be labelled as "unclassy", but you know what? The OP wasn't exactly being classy himself, so I don't feel bad for him. There wasn't even a need for him to make this thread, he could have responded in private to the support team. Instead he made a thread where came off as a hard to please guy who expects to be sucked off just because he's a paying customer, a guy who thinks "the customer is always right" is meant to be taken literally. Sorry, but no it doesn't work that way. A business can't please everybody no matter what.
Alright, I'm rambling and maybe I am being "unclassy " myself. But I wanted to comment since a few people seem worried that the behavior might turn off new customers/users. As a new user, I wanted to say I thought the situation was handled appropriately .

Whether or not the error was his, what he asked isn't the least bit unreasonable. GOG could track whether an account has downloaded a purchase, and offer partial or full refunds for anything that hasn't been downloaded. That they don't is simply poor service.
Further, while the error probably was his, and probably was caused by a disinclination to pay the least bit attention, your speculations about his person is unwarranted. He may well never have been addressed in such a casual manner by support staff before, which may equally well have led him to assume it should be interpreted negatively, regardless of the actual text. He may also be used to having a guaranteed 1-2 week period to change his mind about anything he buys on-line or through mail-order, and incorrectly assumed GOG would let him do the same.
Finally, the assertion that no DD services provides refunds is factually wrong. Stardock does.
Be nicer, guys. Pretty please?

Whether GOG can or cannot provide refunds is beside the point, the "Terms of Use" we all agreed to in order to use this service clearly state that "all sales are final". As such GOG is under no obligation to rectify this person's potential mistake. I am assuming it was a mistake by the OP as they have not responded in the last two days in order to clarify the situation. The original post amounted to little more than a rant and I think the vast majority of the responses here are perfectly reasonable in response to that.

IHe said "ok no refunds fine I'm not heartbroken" so it sounded like he was able to accept that. The "snark" is what he thought went past the line and made him angry.
A few people said the response could be interpreted as snarky, but what exactly was snarky about it? "

If it's put that way, it just seems that he is pissed of at the non-formal response to his problem. His request would be declined any way, but the staff tried to put it in a positive light (as they try with most things that annoy people here), rather than the super-formal robotic standard responses you get from other places. Regardless of the staff's casual manner, they do a great job in maintaining stuff here. I also think it's better for the communication between the staff and customers/community to keep in such a manner.
In any case, I won't comment on the Arx Fatalis thing, because how it ended up in his basket, I've got no idea off, but depending on how he paid for the games, he should have seen the total price, and considering that he bought six games, thus only having to pay for half ($17.96), the additional $6 should have been noticeable before the final agreement for payment.

Finally, the assertion that no DD services provides refunds is factually wrong. Stardock does.
As do Big Fish Games and Valve. (And like GOG, Valve also state all sales are final, but they *do* give out refunds on a case by case basis).
A few people said the response could be interpreted as snarky, but what exactly was snarky about it?
Let's have a look at the response again:
"Unfortunately a refund won't be possible in this case. :( Still, considering the amount of games you got for free in this order, I think it's a fair deal (plus from what I know Arx is a very unique and interesting game). ;)"
The underlined portion could come across as being somewhat "snarky" depending on how you choose to read it. This is simply the age old case of written words not being able to adequately portray actual intended meanings. Take for example the simply phrase "I'm sorry", I'm sure everyone has heard this being said in a sincere fashion, as well as in a sarcastic fashion (especially people in the UK =)) But when written, you can't actually tell by the words alone whether the phrase is sincere or sarcastic.
Likewise, the second emoticon could have misinterpreted as being sarcastic. Note, I'm not criticising the support staff here; I am merely attempting to indicate where a "snarky" comment could be perceived, regardless of actual intent. Besides, the support staff here have been very helpful to me in the past. However, it is best to remember that some of them (at least) are not native English speakers -- a point that is important when considering possible communication errors.

well when you consider that :( was used as the first emoticon and said "unfortunately", it seemed clear that he sympathized with the customer, so as a whole I considered the response obviously non-snarky.
I guess it really doesn't matter. My whole point of chiming in was to tell that I don't think they'll lose many customers over behavior like this and they handled it fine. Maybe they lost a customer, but like I said before you can't please everybody.

The OP essentially said: "I find the service here lacking, enough so that I'll take my business elsewhere. Since you're customers too, here's the basis for my decision."
That GOG could provide refunds, but chooses not to, is half the point. The other half would be the casual tone of the support staff. I agree the former is poor service, but I much prefer the latter to the alternative. You will notice the OP didn't contest GOGs right to behave as they do, he simply disagreed that they ought to.
The OP wasn't terribly emotional. It really doesn't qualify as a rant. In contrast, many of the replies have been borderline rants, highly antagonistic in tone and full of baseless personal attacks.
Then again, I'm often wrong about a lot of things. I just didn't think the guy deserved to have his head bitten off.

Here is the final paragraph of the OP:
"Okay, no refunds, it's $6, I'm not heartbroken. But the snark about a 'fair deal' is a bit over the line. A FAIR deal is actually following through on the promotion you advertised, and delivering what the customer wanted to pay for. Not acting like the customer is fortunate to have to pay extra for something they didn't want because your shopping cart is buggy. I expect I'll get $6 out of Arx Fatalis, as well as the other games I bought this weekend. But in the future I'll be spending my money elsewhere."
This is how I interpreted it; he accepts the lack of a refund purely on the basis that it is of relatively small value, not the fact that he agreed to the "Terms of Use" of this service which clearly states "all sales are final". The use of capitalisation (which is internet shorthand for shouting) is also unnecessary and I completely disagree with his assertion that did not follow through with their side of the deal. They simply charged him for the items in his basket.
As I stated previously this is all based on the assumption that the original poster put Arx in his basket at some and didn't remove it or check the contents of his basket. This is certainly the most logical scenario and the original poster was asked to clarify this point and has failed to respond. Which also leads me to believe that the OP was simply designed to vent steam and not to look for advice, support or consolation.
I understand where you are coming from with regards to the more antagonistic or personal posts, however focusing only on those would be unfair on others who were trying to help or at least give an honest appraisal of the situation given the information provided.

to me the OP essentially said " the support team here is rude, they have false advertising s and their cart is buggy ".
To me that struck me as equally baseless, so I don't have any sympathy for him

To be honest, I'm not even sure why we are still bothering to discuss this. It's clear the OP now has no intention of coming back to see a resolution to this issue -- which further makes the very posting of this topic obsolete.
Mind you, it's also a little disappointing seeing no input from anyone actually from GOG. Even if it is only to state what we all pretty much feel to have been the cause.