Otaku-san is right in that you can often tell a fake UK disc by the lack of BBFC rating, but not that you can tell an import by it. American DVDs are not formally classified by a central body (like the BBFC here or the ESRB for other entertainment). Companies can have their products rated for cinema or DVD if they like but there's no need to and most just make up ratings of their own and print them on the discs or label them "unrated".
Generally though:
If someone says "import" but not where from, it's probably a fake.
If it's subbed/dubbed and labelled as a Japanese disc yet isn't something huge like a Ghibli film or Pokemon, it's probably a fake.
Likewise if it has Chinese language as well as all those options. Actual Chinese releases are usually pretty bare bones and almost always region locked due to the obvious ease of them getting back to the Japanese market.
If it's region free, it's probably a fake.
If it's released by some company you've never heard of instead of one of the known anime companies for that area...yeah.
If it sounds too good to be true, it usually is. Good on the OP for checking though
Like chaos says, a lot of inexperienced fans are tricked by the lavish packaging (not surprising given that they charge £20 per series and pay nothing to make it except a couple of DVD-Rs for pennies). Back in the pre-DVD days the same happened with soundtracks; the infamous Son May and Everanime releases which just ripped off the real CDs
R, who buys far too many things from overseas