How can I spot a fake Jane Norman dress?

I bought a dress from a seller on Ebay and I suspect it's a fake. The description on the listing says the tags and labels were removed for legalities, so there is no logo on the dress and I don't know how I can demostrate that is a fake (provided that it's a fake). The reason why I believe that is that the quality looks poor compared to Jane norman: the fabric is real light and you can see trough. Also, where the label should be, I expected to see some signs of the label being removed on the back of the neck area (stitches holes, for example), but there is nothing, it looks like there has never been a label. I don't want to contact the seller with this allegation if I could be wrong, but how can I judge if the item is genuine? Any suggestions? Thanks