The two key principles of successful haggling are: be prepared (think through how you want the negotiation to go, including your 'bottom line') and be willing to walk away.

First, decide on an upper limit you want to pay for the car you're viewing and stick to it. Take your time over the negotiations, be polite and use the seller's name.

Base your haggling on real faults. The more time you've spent examining the car, the more the seller will be sweating. Recall all those bargain chips you pointed out when inspecting the car. List the things it would need doing to it before you'd be happy with it - couple of new tyres, exhaust nearly needs replacing...any other faults, dents or scratches you noticed along the way. Faults that could lead to an MOT failure in the future are particularly useful bargaining tools. Knock off the price of 12 months tax if it's about to expire. Give the impression you're worried it would be an expensive car to run.

Add up all the faults then knock them off the price, plus a bit more. You can't reduce your bid once made, so start low. Bid at least several hundred less than the asking, more if you're confident.

Expect a look of shock and much huffing and puffing. But don't be bluffed. Look disinterested and leave an awkward silence. Silence is the best bargaining tool there is. Don't crack first.

Most times the seller will come back with a higher figure, but below their original asking price. If they don't, reiterate all the faults you've found. Point out a few similar cars fetching cheaper prices in Auto Trader or other adverts that you've picked out in advance.

When the seller comes back, don't split the difference too early, because now you've got them on the ropes. Make another bid - this time halfway between your last offer and the seller's new lower price.

If the seller sticks to his price, invoke a higher authority: say you'll have to ask your partner, and (what a shock) they say you can only pay what you've offered. Any increases you now concede are worth double their face value.

All the while keep checking your watch and looking concerned. If you claim you have another car to visit very soon, it's not you -v- the seller, but one seller -v- another.

Make a final offer. Get out your deposit cash and let them see it. It still talks. Offer to take the car away that day.

If they don't accept, give them your number and ask them to ring you back if they don't get a better offer.

Do be clear about the tax - is it staying on the car? And don't forget to check it's still there before driving your purchase away.

To read more buying tips, check out our complete guide to buying a used car.

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