As part of the deal on the wifes 4k car last year, the supplying garage said they would attend to any advisories.

If you are spending 20k on a car, i would expect no advisories in the first place

Defo the right decision handing back. Their warranty wouldn't be worth the paper its written on. I'm happy with my main dealer supplied car with extended warranty...I have piece of mind for such an expensive to fix machine