You cannot tell for sure. Nobody can.
If your judgment is based on stats, then I guess you will find out that there're not so many users out there posting on a forum complaining about such a "defect", simply because either they've already asked for a replacement or they're happy with their device in first place. This is not a "huge" defect like dead pixels, color tints or blotchy dark patches for which you can find many discussions on this forum. So, if this is the case, you would probably keep asking yourself "am I the unlucky one?" forever, thus please do yourself a favor and ask for a replacement.
Otherwise please consider this example: if I ask my father to look at my iPad's display he says he can't see the "defect". My girlfriend can. The iPad is the same so who's right and who's wrong?
My point is that you have to decide.
Basing on my own experience (I did it 4 times with the iMac), it's not worth trying to replace the iPad hoping to receive a "perfect" one: maybe you're lucky and would get a better one or maybe not. The fact is that replacement units are usually refurbished products that means you're going to get the device someone else has returned (properly inspected and cleaned by Apple, of course). Thus the highest chance of getting a good one is the one you already had buying your brand new unit. If you're still within the 14 days of "grace period" you can ask for a refund a buy a new one and this is probably the best option, otherwise follow my suggestion: keep it and enjoy your iPad, it's awesome! 🙂