Well the problem is, FSA kept quiet about their vigorelli cranks and made small changes to the interface between the chainring and spider/ platter behind the scene without changing the design at all...
Considering there's easily old stock for such an expensive crank that didn't really sell in the first place and the lack of any official recall or replacement program of any sort, your best bet is serial numbers. That is, if they even had them, to check with FSA.

So yeah, this is more of a gamble on your part. I wouldn't take the seller's word for it either.
If it's a rev. 1 crank and the owner doesn't experience play, it might develop under your ownership.