Haldex diff oil is recommended at every 3 years, regardless of miles, if the car ticks all the boxes I would go ahead with it.
My car had done 50k and according to the digital service history had never been done, so I did it myself and there was hardly any debris on the filter, so I can only summise a VAQ diff is not so hard on the oil as a Haldex diff in a Golf R, which when I last did one, the filter was covered in debris.
For the sake of a sale you would think they would just do it??