I'm buying an Iphone from a reseller.

From all appearances, it looks legitimate to me, but I’m no expert. I am assuming that it was never activated and that’s why you see that message.

I am basing my remarks on a personal experience I had when I bought my wife an iPad for Christmas last year. When I entered the serial number for the iPad into the check coverage website, I got a similar message about the device not being activated yet. Once we set it up for her, then it showed the warranty coverage as I expected that it would.

EDIT - I defer to KiltedTim on iPhone matters. He knows more about this than I know.

Are you buying this from an Apple Authorized reseller? If so, you are fine. There is no warranty coverage until the phone is activated so what you are seeing makes sense.

Looks so.

Then don't buy it. Buy from an authorized retailer or directly from Apple.

If the price is significantly below the normal retail price something is wrong.

TANSTAAFL

Considering that's at least 300 Euros below retail price for the lowest spec model, I'd say that's unreasonably low.