Eames Walnut Stools  

Original vintage
Are somewhat rare... The ones in the link look more recent to me... But the easiest way to tell is from the top.
The reproductions that I have seen on eBay look like crap. Proportions are not the same.
EDIT: I just looked at all the photos inside the listing and see that they are indeed original (or at least earlier) production.

did you see the link that the...
did you see the link that they provide to the christies auction which showed the sale at over 7000!
The licensed repro's are $800.
that is expensive

Here's the same link
in the clickable box
http://cgi.ebay.com/EAMES-WALNUT-STOOLS-GENUINE-1960s-Originals_W0QQitem...

Yes
They are expensive.
The ones in the listing appear to be in very nice condition.

difference
but how can you tell the difference between the originals and the liscensed repros from this day and age.
Obviously the price, but they don't seem marked or labeled?

Top
You can tell by looking at the top. The newer production has a wider and more pronounced lip/edge.

I've had both
... early vintage and more recent production. When you see either one in person you can tell. Generally, it's apparent from the wear and the warmer, mellow color to the wood if they are old. In fact, we have a vintage stool in our living room and a recent production in our showroom. If I remember, I'll bring the newer one home and photograph them side by side so you can see.
That said, if I did not have one, I would not hesitate to buy either. They are a great design and super useful. They can be a table, a stool, you can stand on them if you need to reach something up high... they are small and easy to tuck out of the way if need be. They have a playful, sculptural quality to them. I think they are just grand. Just don't use them as a plant stand. I've seen too many with horrible water rings in the top from over-watering a plant and having it spill over.
They are not marked in any fashion, but I don't think that I have ever seen anyone knocking them off. So it's more a matter of picking either a vintage or newer example. The design has never been changed, they are made of the same material by the same manufacturer. Here I have to relent on my "vintage is best" stance and say if you want one to use, does it really matter? If you don't treat a new one with kid gloves it will look vintage before too long.
Looking at the auction you link to, frankly I'm skeptical that those are really all that old. Most times there is more visible wear, certainly on the bottom. I don't think that I'd pay $2,354 each for two. New they cost $829. Seems like at auction in the US, nice vintage examples have brought between $900 and $1,200.

I had a new one
And it cracked and split at some spots. Now I have a vintage one.

Knock-offs
There was a rash of knock-offs on eBay last year, from one or two sellers. I have not seen any listed in lately.... I think the eBay community cracked down on them. They looked pretty bad.

I found one during a business trip to Atlanta...
off the local Craigslist.Paid about $400.for it.My associates thought I was crazy,as I purchased a duffle bag for it and carried it onto the plane.Upon seeing it wouldn't fit in the overheads or under my seat,an air hostess took it and put it in one of the closets in First Class.One woman in FC complained,"I can't believe coach carry-on is being brought up here!" (The hostess later informed me the "complainer" had been bumped from a previous flight and upgraded to FC on this particular flight.)-Some people!
Anyhow,the stool now has a spherical ceramic sculpture placed upon it,and looks great next to one of my Eames chairs!

Here you go
Knock-off.
http://bit.ly/9XSd26

Set of 3 genuine Herman Miller vintage walnut stools at Christies
Hi everybody,
Been following this forum for a while but this is my first post.
So check these out, they look the same to me? Will be interesting to see how much these go for!
http://www.christies.com/lotfinder/lot_details.aspx?from=salesummary&int...

Check out how much they sold for!!!
The stool on the right has cracks to the joins and they have a lot of wear, yet they still sold for £6250 / $9369!!! WOW!!!
Seems like they always do well at christies?
They say they are original herman miller versions, but no date, just a design year.
They look a lot lighter than the new ones and personally, i think vintage is best! I like the wear to them, shows that they are genuine I think. New ones could look like repros...
Take a look here:
http://www.christies.com/LotFinder/lot_details.aspx?from=salesummary&int...
http://www.christies.com/LotFinder/lot_details.aspx?from=salesummary&int...

Impressive
Yes, those are vintage as indicated by the less pronounced lip around the top edge. And the lighter color as you noted.
The fact that the auction was non-US based is probably a key factor in the price. I got mine for about 400.