There's much less leeway for a used car than a new one.
Depending on whether a dealership group meet their volume sales and customer satisfaction targets, they can get a new car for up to 30% less than list price. They just need to sell it and have the overheads of the dealership, the sales people's time, reception, keeping the Flavia machine and Lotus Biscuits well stocked and a portion of the workshop's time for PDIs etc (and a few other factors I haven't considered). The new car coming in isn't depreciating until it is registered and considered used. If a car comes into stock without someone specifically ordering it, they can put off registering it until someone decides to buy (within reason).
Bring in a used car in p/x for maybe 65-75% of probable sticker price. It needs an MOT, the 2 front tyres are a bit low, needs new ones to appeal to buyer, it's out of warranty - £300+ to give a year inclusive warranty, one of the wheels is badly kerbed, replace it...and it's depreciating at a certain rate a month for all the time it doesn't sell. Plenty of opportunities to make a loss or a poor level of profit if the car hangs around.
You're far more likely to get a decent discount on a new VW than a used one, and a far better finance rate if you need finance. For me, it's not worth buying a nearly new VW for coppers less than you can buy a new one.
There's a fine line between a cheeky offer and an offensive piss-take price.