If it's too good to be true, it is NOT always true... probably just most of the time. I got a steal of a deal on eBay for my brand new MBP a few weeks ago...saved about $700 rather than going through Apple...even with their student discount.
However, whenever you see the "email me before bidding" message... it is 99.9999999999999999999% of the time a scam. There's no reason they'd ask you to email them outside of eBay, other than their eBay account being hacked. The hacker doesn't have access to the eBay account's email address, so they ask you to email them at their address instead. Then they'll ask you to just paypal them, or whatever their shady plan is.
Use eBay, use PayPal, and only buy from buyers with lots and lots of positive feedback who have been a member for a while, and have other recently completed listings for which they have received positive feedback.
If you use eBay and PayPal together, you are 100% protected. The only thing you could possibly lose is a little time.