When dealing with a retail goods, your first contact should be the store.
An Approved Used automobile is often supplied with the guarantee that the AU warranty is provided by the manufacturer and that you have the backing of the whole official dealer network.
Although the OP's use of several dealers does not contribute to their argument, the main purpose of the MB AU plan is to allow customers to purchase a vehicle in Truro and get servicing in Inverness.
Indeed, with reflection, some individuals may choose to decline accepting a vehicle if they see a warning light upon its collection. However, this approach is not universally adopted, particularly among those who are encountering such a circumstance for the first time.
Regarding the automobile, the original poster (OP) must determine what is acceptable and what is not. Wiper judder is an irritating occurrence that is likely to divert one's attention. The issues that have been rectified are now completely fixed, and they may also be seen as a diversion. However, the malfunctioning of lighting and electrical components is a matter that requires prompt care throughout the warranty term. If there is an unresolved underlying problem, it should be calmly raised first with the individual dealer and then with the manufacturer, MB. In the case of a potential misunderstanding, both the dealer and MB should be capable of providing a clear explanation.