I "figure it out" before I buy. I also buy towards a collection theme or goal, not randomly. That way I avoid buying a lot of ballast. But that's just me.
The Lawnchairs were also made in 3/4" dia., however these are harder to find. One of the people that was there for the run told me that the ~5/8" were far more plentiful.
White paper will cause the opposite problem. As Chas suggests, choose a background that is neutral - neither dark or bright. The method I noted earlier solves the problems of both focus and exposure (mostly) regardless of background.
Your camera is exposure-averaging based on the background, which is dark. The result is the marble is way overexposed.
If you manually choose center focus, the exposure should be much better.
Most of these are not "9.9". If you described them anywhere near that and I bought them - I would return them shortly after opening the box.
Accurate identification AND grading are important.
What you are referring to as a "fish eye" is created as the molten (read: not solid) glass spins down the rollers. It is a completely circular motion. Note the circular motion in the glass.
My special thanks to the men and women of our Armed Forces who are deployed far from home where it feels very little like Christmas. I've been there and done that. Your sacrifice is important and well-appreciated.