Petrol-head question

Are Parkers Guide prices way under? Or are dealers massively overpricing because they think you'll haggle them down? Or are South-East prices just generally higher?

E.g. Parkers reckons around £1,600 max for a 1998 Civic 1,5GXi. The prices I'm getting in Autotrader are from £500 to £1,000 higher.

It's ages since I've done this...