Autotrader look at Make, Model and Mileage - the end.
No consideration for:
Desirable colour (change the spec to an expensive option)
Number of Owners
Service History
Tyre Condition
Condition Generally
It is a complete farce.
Plenum chamber underneath the battery, there is a little rubber flange that clogs up. Remove said flange and throw in bin.
If you have access to a ramp this can be done underneath by a young lad (watch him get drenched)