Details is a grade though it's just not a straight grade. Their listings also say in bold letters in the description they only guarantee authenticity. They also say their return policy is 30 days which is a long long time for coin sales and that has passed as well. If they want to take them back that is certainly their right but I do hope eBay doesn't set a precedent that will impact other sellers by forcing a return if they don't
I only raised the subject because shilling is one of the possible explanations for a buyer doing a large percentage of their bidding with a single seller. That was a lead-in to responding to your question - yes, they_do have a large number of loyal, repeat buyers and your thinking about why they get good prices is correct.
Please allow me to quote from the description of one of the coins purchased (which is widely used by this seller)... "We guarantee AUTHENTICITY ONLY!!! We do not offer grades on raw coins, and we do not guarantee grades on raw coins. If you are looking for certified coins, we offer a wide selection of PCGS, NGC, ANACS, and ICG certified coins." As much as I sympathize with your disappointment, you're ignoring what you don't like or that doesn't suit your position in favor of what could bolster it if looked at emotionally as opposed to logically. First, something tells me if you had purchased a coin advertised as "AU+++" that turned out to be AG, you wouldn't be anywhere near as accepting as you claim, but I digress. Is an "AU details" or "MS details", or (as an example) ANACS and their ridiculous "AU58 details" not a higher designation than, say, "VG details"? I realize that the ubiquitous "AU+++\BU" type claims on eBay can be misleading, but I - and do correct me if wrong - don't recall any direct claims of a straight/clean number grade. Again, you interpreted the descriptions to be what you wanted to see and not what they really said, and is a mistake a regrettable number of people seem to make. You also dismiss what I said about learning and knowing what one is buying, but as baseball said, you had the coins in hand prior to submitting them, so even with GSC's overly flattering photos, you indeed had the opportunity to decide for yourself if they would pass muster. It simply is not GSC's fault that you either didn't bother or weren't able to do so for yourself, and instead decided to submit them not at a level that would (may) have gotten you the results within the return window, but I assume at a cheaper level that most likely wouldn't. Of true, this was a CHOICE you made, sir. A 30 day return window for a coin is already wholly ridiculous and is something that doesn't happen in the real world without a prior agreement between buyer and seller, yet you decided to ignore it and the excessive benefits it allowed you. Had all worked in your favor, it would've been a smart money-saving move, but because it didn't, the blame is rightfully yours to shoulder. I mentioned the liberal return policy earlier for good reason. Often in these threads someone brings it up as if a positive for the seller, but in reality they're not doing it out of the goodness in their hearts, or in the name of customer service. When you sell a large number of higher dollar problem coins as they do, easy returns is the most obvious way to keep otherwise steaming customers happy. It's an old, well-known, and widely used business tactic, especially in areas where repeat customers are of absolute importance. You state GSC "bears responsibility", and they most certainly did within the allotted return window, but I can't help but to wonder what you see as your responsibility in the matter other than to possibly/hopefully reap the rewards without shouldering any of the risk. Where was your responsibility to know what you were buying when you first held the coins in your own hands, and where was your responsibility when filling out the submission form? I understand very well that when things don't work out as we hope, it's all too easy to blame the other guy, but you had a huge window in which to learn the facts and apparently decided to ignore the opportunity. I'm genuinely sorry for the situation you're now in and that the coins are not everything you had hoped, but the fact is you're not an entirely innocent party and rightfully shoulder a great deal of the blame.
Now that the original poster has been thoroughly chastised, I'll volunteer for my licks, too. I have been watching GSC for a year. I finally bid on the proof shown below. Yes, I went through all the GSC threads from years past, and yes, I checked the eBay comments for the seller. The point of my post is just how the photos may look different from the coin in hand. First theirs, then mine. In hand you can tilt the coin and see the mirroring off the fields, and nice coloring. This is closer to reality. So I'm not sure what my point is. The poster already said he is happy with 75% of his purchases from GSC. He had the coin in hand to look at. There is a generous return policy - plenty of time to go to a trusted dealer and get another opinion. And finally, their photos have a consistent style. Once you learn the style you can still deduce a lot about the coin. They may be those who denigrate GSC, but in all truth, if you treat them as one more resource at your disposal, and learn their language, there is no reason to dismiss them totally.
It is difficult to tell from a picture. I would like to hold the coin in hand to see for sure if it was cleaned or not. (I don't think Soiled will let me because I may like it and not give it back.) But under the lighting that the graders use - they also have the benefit of holding the coin - they may have seen something. I don't think its whether the polishing lines cross, I think they may. It is just the overall look of a polished die striking a coin and imprinting the die polish lines with 2 tons of pressure versus post-strike cleaning lines: they simply look different. (Someone correct me if I am wrong.) One thing is for sure: this is "a good teaching opportunity for someone!" but I am not knowledgeable to be that "someone."
I am not very experienced with coins, but the 2nd picture Looks like the oil from soap. I am not sure though.