E.g., you're looking at a rich MBA. Say 100,000 MBAs graduate a year in the US. You still don't have enough information to know if he was any good.
Worse, say you use a pedigree: You're looking at a rich MBA from Harvard. Say they only graduate 1,000, but, because any damn headhunter will put a harvard MBA into a C-level job, 90% of the harvard MBAs stack up a ton of money. Now, knowing that he's a rich MBA tells you even less. All you really know is that richness & a harvard MBA seem to correlate, which is kind of exactly where you started :) (on the other hand, if you had a poor harvard MBA in front of you, then you'd really have something!)
Anyway, yeah. it's a really hard problem -- just as hard as finding a good programmer, imho