We're not saying investigate EVERY part, but comsumables and wear and tear items, like brake pads, brake discs, clutches, tyres, belts, go on forums, research common faults, average intervals of clutch changes, ask if any forum members live near and whether they fancy coming along to have a look at the car with you (sounds odd, but it has been done before)
And yet you still go there.
Look, either get the refund if that is still an option, or sell the car on privately and take the hit or bite the bullet and take it to an independant garage and get the Zed sorted out.
Sure it's a pain, but hopefully once it's sorted, you'll have stress and worry free motoring, plus a good independant will prolly know more about the Zed than a Nissan spanner monkey.
Good luck with everything