I've shipped several items sold on Ebay to Greece over that last year or so. The only "customs form" you'll have to complete is the one furnished by Ebay when you select "Awaiting Shipment" from the "My Ebay Summary List".
If it's similar (and I expect it would be) to the one we use here in the U.S., you need to sign it before shipping. Th epostal service will stamp it with date and approval and give you the bottom half as a receipt. The description of the sold item is automatically printed from the descriprtion you used to list it on Ebay, and I've found some times that you get a message when trying to generate the Form that says something to the effect of too many words. You'll have to insert a shorter description but that's easily done.
What I do find though, is the European buyer will often ask me not to describe the item thoroughly and to declare it as a "gift" (one of about four selections that you have to check. I never fudge on the description and always select the box titled "Merchandise". Apparently they buyer is trying to avoid import duties or some such.
I've never had a problem, but most of my sales have been vintage Ray Ban sunglasses, so maybe they're not seen as provocative...