I recently had to open a SNAD. It is very simple. At first you are asked to communicate with the seller (but through the PayPal dispute system), so you write as if you are speaking directly to seller. Probably repeating to him/her what you have already said when dealing with them directly. They may or may not respond.
If they don't respond, or respond in a negative way and there seems to be no way forward, then you can escalate it to a claim. PayPal may then ask you to provide proof that the item is not as described. They usually want it to be assessed by a dealer or auction house with a substantiating letter on a letterhead confirming it is not Whitefriars. They MAY accept a link reference to this thread, but unlikely. So you need to know a friendly "professional" who will supply you with this info. In my case, the item was broken, and so I pre-prepared a letter on the lines of "I have examined this item and confirm it is broken etc etc" and asked my local Antique shop to sign it and give me a letterhead or compliments slip. This then had to be faxed to PayPal. I got a full refund.
In another case I got my refund in full from the seller before having to escalate it to a PayPal claim.........I think it is worth doing because the seller doesn't want the hassle or negative feedback,so if they think you are serious then they capitulate.
But this may all seem to much for an item for which you may have paid very little, I don't know, and sometimes you just have to put it down to experience. Emmi