This is perfectly true of grey market reps, so don't worry about that, however, it does mean the value is less, and therefore I would not be paying 700 potato chips, wotsits, or whatever currency you are talking about (presuming USD).
Exactly, resale value of a grey market, especially without papers or box is very low. As Pug has said walk away from this one.
The best advice about purchasing a rep, if you want it buy it, if you're not 100% sure, then you need to wait before you purchase it. Flipping gen watches can get costly.