Some DVDs are very poor, the DVD of The BBC4 series "The Detectorists" was widely derided in these forums. It is probably not a fake if you bought it from somewhere respectable in which case you should have no problem getting a refund.
You could try the TV shows: US forum as I'm sure that someone there will have bought it.
Just found this on the Amazon site for the series 6 DVD, hope it helps.
3.0 out of 5 stars Fantastic series - Awful picture with DVD set, 30 Sept. 2016
By Mr. Christopher Watton
Verified Purchase(What is this?)
This review is from: The Walking Dead - Season 6 [DVD] [2016] (DVD)
I love this show, I think it is one of the best horror TV series' ever produced.
However, the three stars are for the DVD boxset picture quality. Quite frankly, it is awful. The picture is grainy and looks more like something copied from a VHS video cassette.
I thought it may be my player (PS4), but when I compared the picture quality with the new DVD release of Scream Queens (ordered both together), and the difference in picture quality is like night and day. Scream Queens' picture in pin sharp and colours are vibrant, whereas the Walking Dead episodes look washed out and detail hard to discern, and TWD box set cost almost £10 more than Scream Queens. Should have ordered the BR version, I guess.
Am I the only one with this problem?