The $700 option may include a package of sorts – one with a lens maybe. The $300 option may include only the frame without the lens. If you’re confident that you are buying the same product at both places, though, there’s no reason to pay more for it.
References :

http://www.resellerratings.com/store/Bingo_Cameras
http://www.resellerratings.com/store/Stop_and_Shop_Digital

B & H and Adorama are probably the most well know camera stores compare with their prices.
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There’s one sure way to tell a scam page and you’ve just mentioned it. When the entire world is asking aroud $700 and one comes along asking half that you can be certain that all they want is your credit card number.

If you order one of those the first thing that will happen is you’ll get a message that your camera is on back order – you will never receive it but you will be charged the money and they now have your credit card number.
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That is what is referred to as a bait and switch. They draw you in with a low price. You make an order and then receive an email asking you to call them or they call you "to confirm" your order. Once they get you on the phone they try to talk you into buying "accessories" that are supposed to come with the camera, like a battery and charger, at exhorbitant prices. If you refuse they will then tell you the item is out of stock and cancel the order. If you make a purchase and are unhappy it will take weeks to get your money back so you can make a legitimate purchase.

Save yourself a headache and buy from either a local camera store or someplace like B&H or Adorama who have great prices, shipping costs and customer service.

If you are tempted to buy from an unknown seller, check them out at resellerratings:
http://www.resellerratings.com/store/Bingo_Cameras
http://www.resellerratings.com/store/Stop_and_Shop_Digital
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The sites offering the T1i for a super low price are scams. Thieves. Dishonest.

Always check any seller at http://www.resellerratings.com
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