You should be able to find the tasks and consumables for the service schedule online, print it out, highlight the "must replace" parts for that particular service and take it with you. Make it clear when you drop the car off that you do not want any parts except those highlighted fitted during the service, if there are any other parts required the garage must contact you and receive authorisation, if parts are fitted without consent you won't be paying.
Other things to watch are charging you a fiver for a bottle of screenwash - fill this up before you go in and get them to take it off the bill when, inevitably, they try to charge you for it. Replace your wipers yourself and tell them they're new. Also when the garage charges you for a full can of grease for door hinges etc. make sure they give you the rest of it, you can then spray them before you take it in next time - I'm still using the can I got from a Passat service in 1999!!
Alternatively, find and use a good independent.
Good luck
SSE