Agree, it looks like a young, washed out Vieja argentea.
Be advised, they can get aggressive with age, they seem to ignore small fish, but don't like to be with similar size, and color cichlids.
He looks sick the LFS guy knows it is rare so he wants 30 bucks. I told him I would give him 25. It has fin rot and some growths on his fins and he is not swimming normal either. I had to pass.