...I hardly see the difference between a 'MS-63' and 'MS-64'. But the price difference can be thousands of dollars, or even more ridiculous.
I am an opponent of third party grading. It does not benefit collectors. I agree with Arthur (akona).
Sending coins away to be graded by a third-party is definitely one way to grade coins, but I was really hoping we could talk about how we grade them ourselves, and about the grading guidelines we use (or perhaps
will use).
But briefly, on the subject of third-party grading, I agree with you about hardly seeing a difference between MS63 and MS64, and when akona20 talks about the games that go on with third-party grading I'm definitely in his (and alglasser's) corner. (I thought alglasser's last post, especially, was really worthwhile.)
If MS60 is defined as (just) Uncirculated, and MS70 as "Perfect" Uncirculated, then we know that there is a continuum of coin condition between MS60 and MS70, and we know that MS63 and MS64 are two different points within that range. Makes logical sense. But can we consistently see the difference between these two points? I can't--but then that's not the kind of collecting I'm personally interested in, and besides that, I know there are collectors out there who are a lot more discerning than I am. So I'm more than willing to accept the idea that third-party graders and some collectors--and investors--are playing games that I want no part of--but then I also know there are third-party graders and some collectors--and investors--who are able to see things in coins that I can't.
But I
can consistently see the difference between the major stopping-places that are commonly used: MS60 (Uncirculated), MS63 (Choice Uncirculated), and MS65 (Gem Uncirculated). And MS70, or nearly so? I think I can see that too, and do with some regularity, in some of the world's Mint Sets. (The British, apparently, and some other folks too, call them "BU."

)
Anyway, these are differences in UNC coins that even I can see, and among the major third-party graders at least, what I see slabbed pretty much comports with the understanding I have of these grades.
As cmerc so correctly points out, the original purpose of third-party grading was to authenticate; it's something they do still, of course. And the occasional horror story notwithstanding, competent third-party authentication is becoming more and more useful (
worldwide) all the time. (To investors surely, but also to collectors.)
And then there's that other undeniable benefit to collectors rendered by competent third-party graders...AU58!!

v.