Car supermarket or ford official dealer?

[noarguments]

Am looking to buy a used car, am comparing the same car at ford and a car supermarket, and the supermarket is quite a bit cheaper. The ford salesman tells me that I'm better steering clear as supermarkets often have lower quality cars and have added costs. He would though, he's doing his job. Is he right? Am I more likely to negotiate a better deal at one or the other? Thanks for any tips.

He would, wouldn't he, as you say. The car supermarkets have a far better reputation than the dodgy second-hand merchants of old but, that said, if you are buying very nearly new you might be better off sticking in the official network as you'll (probably) have more comeback if something goes wrong.
It really all depends on the price differential; say the Ford dealer wants £9k and the supermarket wants £7k. First off, how much haggling can you do? Dealers often prepared to drop more than supermarkets as margins are higher. If you can bring the differential right down then go for the Ford dealer.
Second, if there is still a £2k differential think of this as the cost of insuring yourself against the potential extra hassle of getting faults rectified by the supermarket over and above the same with the Ford dealer. That's a lot of money for a bit of extra peace of mind.
Whatever you do, don't be seduced by nonsenses such as 'free' car mats and the like. If someone is prepared to chuck in servicing for a year or free insurance though, that's a different matter. Go in hard. It's a buyer's market. Unless you are buying something rare and expensive there will be a thousand alternatives out there and the dealers know that.

Thanks, that's kind of what I thought, better get my haggling hat on then.

Ford dealers don't have the best reputations. My last dealings with our local Ford dealer didn't impress me at all.

You might get a little more comeback with a main dealer, but probably not enough to be worthwhile. I was sold a lemon by a Volvo main dealer and found both the main dealer and Volvo customer services pretty useless.

All in all I would say the the reduction in price from buying in a car supermarket is probably worth a lot more than any notional main dealer support.