Even money says that seller has already been busted.
How many people had exactly that many earned upgrades, lifetime miles, current mileage balance, YTD segments, etc. on that date? Answer: exactly one. And AA's technoweenies probably zapped his account. (Even a newbie mainframe hack with an SQL book could figure it out in ten or fifteen minutes.)
Even if I wanted to buy his miles, how would he turn his 947K into 500K for me? It sounds to me like he'd have to order travel certificates for you for flights that total up to 500K worth of award travel. (That's a lot different from having 500K in my account, counting towards my lifetime status and available for use for int'l upgrades at booking time.)
Basically, the whole thing stinks, and the guy laying out $6600 will get jammed.
As for his other verbiage about a partner to earn unlimited cheap miles, I don't buy it. I think he just wants a repeat buyer of his excess miles. Look at his YTD segments/miles: 38,000 miles, 12 segments, 2 1/2 months. This is an ExPlat that flies full-Y for business on a regular basis. Now look at the earned upgrades, combined with his statement that he likes to use his own upgrades (meaning he's earned a lot more than 42 in his life). I'm guessing this guy has earned 500-750K flight miles. Assuming he was PLT most of the way, there's most of your 1.5 million lifetime.
This guy doesn't have a sneaky loophole, and he doesn't have a secret way to earn cheap miles. He probably doesn't even know Flyertalk exists, or else he would have read enough threads like this one to know not to post a freakin' screenprint of his account on Ebay. While I think there's a 95% chance this guy is a rat, I suppose he might not even know that AA disapproves of his auction - until he gets an email.
He simply flies a ton on somebody else's nickel, he can't use all his miles, and his "partner" would be somebody who always goes through him to book travel (buying his miles).
Unfortunately, it looks like he has found at least 1 sucker.