wait another couple of hours and the price will drop once the iPhone 7 is officially announced and will drop even more in a couple of weeks when its released
You take a bit of a chance, but you're well protected if you buy through paypal on ebay. You need to make sure that its been properly wiped, which releases it from its former association with an apple_id. If you buy one that still has that association, it may well have been nicked - its worthless as it can't be used.