I'd be asking myself the question, why is he selling it?
If he's paid less than £30 and is really happy with it why the rush to sell it on?
My experience with these rifles has ranged from negative to extremely poor. I haven't shot any of these rifles at consistent groupings, I've never seen two rifles, together, that will chronograph the same. Sure they're cheap enough but I wouldn't be confident trying to take live quarry with them.
If you're looking to buy it, think long and hard. Have you seen this rifle perform, to the levels that are claimed or are you taking his word for it?