I'd prefer to see the hallmark rather than take the sellers word for it. The photos are pretty small and blurry, but if you find the hallmark, maybe you can post a cropped high-resolution image and we can help you. 500 euro would be a fairly conservative value for the gold value of a 14k watch. Obviously, that is a substantial portion of the total value. Sorry if I missed it, but how much is he asking for the watch? Is this a local cash sale from an owner?
Anyway, assuming it's solid 14k and you like the day-date format (it's not my cup of tea), then it would be worth buying at the right price. If you're new to vintage watches, just be aware that you should assume it will need a professional service, so figure that into your budget.