I'm not sure sure that dealers rely on WBAC's prices (I take it that's what you mean)^ No I mean that's what dealers use these day for PX values, normally they'd go £50 higher and say well this all you'll get from this lot, and then discount £100 of the car.
When I ditched my CTR for the Clio the Dealer I was buying the car from Offered my £4200 PX and I pay Full wack on the Clio, effectively this was £200 my way but told them to f**k off it's a 7k car and they are taking the piss, then he turned his monitor round.