When I send my car in for servicing at P2 Glenmarie, I always ask on what parts/fluids/consumables are to be charged for the service. Strike off the ones you don't need, such as windscreen fluid or magnet traps, and ask them to call you if they want to add any additional service items.

Most of the staff there do have a conscience and are 'aware' that they are pushing you stuff that you don't need, so politely informing them of your specific needs isn't as difficult as one may think.