Jeremy Clarkson would have a field day...
I do sympathise with you as I had similar bad experiences with Ford (tho I was 21, naive and spending pittance on a tired Fiesta) and it seems your dealer isn't the best. Also my experience of Renault dealers is not good to say the least, so I stick with independents or non franchised Renault specialists. HOWEVER....
Are you telling us you bought a car,
Without opening the boot - this would of shown you the parcel shelf and light faults
Without opening the bonnet - this would of shown you the clip fault, and also any signs of respray or damage
Without trying the wipers
Without trying the lights
Without looking at the service book or log book - one look at the words "rental car" would have most of us shutting the door and saying thanks but no thanks. Its no use questioning the mileage once you've handed the money over unforunately, the time is when you are looking it over.
One other point - Autocentre may have been telling the truth, but free safety checks are not usually free - they need to find things wrong in order to get business off you. They may not have been, but this could explain your mechanic at renault not finding the same faults.
I don't envy you, and I hope this doesn't seem too harsh, but dealers are there to get YOUR money - there are thousands of cars out there and they are fighting for your money. Make them earn it - take as long as you want to check the car over, refuse to put a deposit down or sign for it until they repair the faults, be prepared to walk away. You will be surprised how much more helpful they can be then.
Once you have handed over your money they aren't particularly interested - they will do their bit to keep you happy, but your position of power is when you are waving the ££££'s in their face and saying "you can have this if you fix a,b,c, otherwise I'm walking down the road and your mate can have the commission instead"...