The problem is not 'eBay'.. don't blame 'it'.
The problem is the venue .. any method of product sales sight unseen via listing like that is bound to have it's fair share of unscrupulous vendors.
But, with Apple product, unless there is an end user who is just unloading something due to dire straits. Apple product is so extremely price controlled, about the only thing you may see being used as a loss leader is the iPod. Do you think for just one second that if someone can sell a Mac on eBay for $100 less than Fry's, CompUSA, store.apple.com, Small Dog, etc - that those stores themselves would do more than discount each other by a couple three bucks here and there?
Fishy with a Capital F.
Using just your basis of "they have 112 feedbacks, they are a Power Seller", etc... a Power Seller with only 112 feedbacks? They must have just gotten that.
there have been many stories of scammers building up their reputation over many months, even a year or two before going on the big scamfest and then vanishing.
What are the payment types? PayPal, Credit card, fine. Bank wire, Western Union, some weird arse funky escrow company in Romania? Run like hell, Think of your extra $100 is insurance that you will get a MBP that you have full access to all warranty services and options.
Again, there is no valid reason other than an individual (whom wouldn't typically attain 'power seller' status) that is willing to loose some dough to recoup their losses in an urgent/dire situation.
...but needs vs. wants, and narrow vision due to a magic $100 'saved'.