Some information here: http://www.ngccoin.com/price-guide/world/spain-12-escudo-km-4251-1786-1788-cuid-8439-duid-0
I'd certainly say he is, about twice what it is worth. Tobiask, add this link to your bookmarks - http://www.acsearch.info/ Once you register there, and yeah it's free, you can see stuff like this - And if you select one of those coins on the left, this is what you'll see - I'm just using those screen shots as examples, I think you get the idea.
Personally, I am skeptical of any seller who lists a coin as certified, but does not show the holder label or cert #...I feel they're hiding something.
Very true, i refuse to purchase coins with hidden cert numbers. Always fishy. Those are the same people that take close up shots of tiny coins, not stating the size and making them look large to fool buyers..