Somebody offering me too much on eBay , seems like scam?

[Sean]

I'm selling my working water damaged iPhone 5 on eBay , started it at 370, which I thought was kinda high. I just received a message from an eBay user. They asked if they can pay me 670 for the phone , I don't get it. Why would somebody want to pay so much more. It seems suspicious. How do I figure out if this is a legit buyer.
Well I don't understand how I would sell it to him for 670 when the auction has it at 370. Do I end the auction and tell him to pay me thru PayPal? I was always used to bidders winning an auction, then paying right there on eBay . Is there a specific way I should tell him to pay me? I've just never had someone send me a message and offer more (way more) than the asking price
I think I'll just leave it alone , since new iPhone go for the same price . Seems fishy