ID eames chair?  

modernica is still making fiberglass shell chair so the seller is misinformed...
if it is indeed a modernica piece, it would cost a few hundred dollars for a new one.

Hmm
The sanded stamp is curious. Where are you located?

Located in Spain
I'm located in Spain and the seller is an importer of US objects (chairs, lamps, etc).

pibe,I'm not familiar with...
pibe,
I'm not familiar with how Modernica marks their chairs, but it's possible the dealer is importing Modernica chairs and deliberately sanding off the markings and passing them off as vintage Eames chairs. I have never seen an authentic Herman Miller/Eames fiberglass chair with a stamp even remotely similar to that.. Whats the name of the shop?

it's a dealer
the seller is a dealer who brings a lot of material (especially from the eames) and then sell it to stores. Usually brings the chairs just with the shell and then puts a new base.

Doubtful
I doubt that that is a Modernica chair. Their shells use large shock mounts and have a large MODERNICA embossment. Also, the scam would not be cost-effective unless the seller is really able to sell the chair for $1500. Even in Europe, a vintage Eames shell with reproduction rocker base is not worth that much.
The shell in question looks slightly off to me. The back seems a bit too tall.

logo image url
just in case you can't see the logo correctly, this is a better the image url:

does the partly sanded logo...
does the partly sanded logo look like any legit one??
also the edge looks a little thick in my opinion and the shockmount seem rather new..
a legit armshell with a repro base is usually about 550? on ebay in europe.

Woodywood,If you look...
Woodywood,
If you look closely the shockmounts look like theyve been replaced. Perhaps to remove the Modernica embossed versions?
Also, a vintage Eames rocker can easily go for $1500 in Europe.

Sorry
I meant the shell itself is embossed with a large MODERNICA.

Too many red flags.
Why would anyone want to obscure the molded-in ID if not to deceive? The rest of the chair looks too fresh to be vintage. And that color?

Wouldnt...
Mind betting the belt sander that has been put over the suspicous tag, has been run around the rest of the chair as well to give it a fake 'used/worn/vintage' look. If I were you, I would look to spend my hard earned cash else where, and buy from a good european dealer. Granted it may cost a litte more in shipping, but will be well worth it, as you will have the real original chair to put in your house.

looked up photos of...
looked up photos of modernica shells and the embossed logo seems to be right between the 2 front shock mounts.
could it be from whiteonwhite? do their knockoffs have shock mounts?

Comparison with a chicago eames version
I made a comparison of fiber density with an official chair from chicagoo factory and I can see much difference. I have some relationship with the seller and would like to show him where it comes from... Think it's a scam... As freedomBigelow suggest, does anyone know whiteonwhite logo?
Also the story the seller told me that the eames did mass series for hospitals and universities, anyone know anything about this?
Thanks