Do you have a really good digital camera? If so, I'd be inclined to email him some very large pics showing the card at various angles to a strong light.
I don't think it's buyer's remorse exactly, but some people are very persnickety when it comes to cards, and some of those people live overseas.
A bigger problem in my mind is that this tends to be the sort of person who will gasp in horror when they have to pay customs fees. So, while giving a very detailed description and very large pics, I would also state firmly up front that the item will be declared as merchandise and that the buyer is responsible for any customs fees which may arise.
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