Does the ebay buyer protection apply if an item is described as 100% authentic and is fake

[reallynicestamps]

http://resolutioncenter.ebay.ca/

Yes. If you believe it is counterfeit, file a Dispute as "not as described".

EBay will probably require you to return the item, fake or not, to the seller. If so, use a Delivery Confirmed shipping service. This can be expensive, but you will not win unless you can prove delivery. Not shipping, delivery.