What questions should I ask before buying an OEC?

[I like ice]

I am considering a "pre-loved" OEC which is currently set. Since you can't determine cut "by the numbers" for stones like this, what questions should I ask? The seller is a longtime PS'er with a good reputation so I am comfortable with that part. My main criteria are spread and fire. I am very open on color and only care about "eye clean", not mind clean.
Any guidance is greatly appreciated!