Thanks for the reply.
Because I agreed a price for the car as advertised with Isofix baby car seat adapters and it did not have them. Is this not mis advertised so the original agreed price invalid.
Also the fact they sold me a car with a live shotgun cartridge under the back seat. (they would have found it if they had cleaned the car and checked for the Isofix). have any bearing on the outcome. It could have gone off if it had slid and hit the seatbelt mounting.
Thank you for the reply. In this case I will just keep quiet and hope the don't notice. If they do I will tell them about the shotgun cartridge and how they don't deserve the money. Would it be better for me to pay as soon as they ask or wait to see if they try to get it. And last of all is there any time limit for them to ask.