I have not done a ton of business with Metro/ComicConnect, but my results have been mixed. My first few purchases from Metro were great. The grading was spot-on, with one or two even undergraded by at least a point. The prices were great on all!
However, my next purchase was a mess. One comic had a detached cover (not disclosed), another had a rip that went through the entire book (the listing disclosed the rip as being on the front cover only), and another book they called a Fine had multiple stains on the front and back covers. They did offer a refund, but I had purchased them as a gift, and they arrived just in time. I'm more of a stickler on condition than the recipient, so I let it slide.
More recently, I had a negative interaction with a rep from ComicConnect after their recent auction ended. I won't get into the whole thing here (I already posted in another section), but a slab arrived cracked. It is a small crack, but I'd expect a purchase of several thousand dollars to arrive undamaged. I'm not sure if the packaging was the cause, but the three slabs I purchased arrived stacked together, with just a bit of brown wrapping paper between the slabs and the box in which they were shipped. When I brought the cracked slab to the attention of the CC rep, he replied in a very unprofessional and sarcastic manner. I sent a letter to Stephen Fishler to inform him of this employee, Brandon Peck's, very strange and unprofessional response. Stephen Fishler responded and asked when I could chat. That was two weeks ago. I replied twice with my phone number, and he has yet to respond. My experiences (at least so far) with Heritage and CLink have been much better. Perhaps they do not have the same cache as far as Golden Age, but they are much more professional and responsive when it comes to customer concerns.