If you look at the sellers feedback over the last 12 months, he only has 2 negative feedbacks. One of these however was for a 'new' Nikon camera which arrived without warranty card or manual. When the purchaser tried to register it with Nikon, he was informed that it was a grey import and didn't therefore carry a warranty. If you decide to purchase from this seller it would be worthwhile checking that the camera is a genuine UK one before parting with your money.
OnePlus 5T review: Hands-on