According to the German law, the tax trick works only for the labour fees, not for the parts and consumables (filters, oil...). Plus you might need to hire a car from the dealer to go back home (costs around 40 euro), but in the end it is still cheaper than the service in Switzerland.
You must also check your warranty contract with VW, it might be that you must service your car at a swiss VW dealer in order to retain the warranty. In my case (I have a second hand 2004 VW), if I service my car in Switzerland I can have the Total Mobil road assistance for free.
Anyway my experience with the swiss VW dealer is bad: too expensive, slow and incompetent (they did not reset the OBD from the many alarms it had, they had to call in a guy from VW Germany to fix a problem with the engine). I have TCS road assistance so I will not service it again in Switzerland for the Total Mobil assistance, I'll go to Germany or Italy next time.
After nearly forty years in practice, a gynecologist decided to retire to pursue his first love, auto mechanics. He enrolled at the local community college and worked very hard, but worried that he was too old to compete with his younger classmates. Sure enough, on the final exam the other students finished in about two hours, while it took him the full four hours allocated. Afterwards, as he washed up, he asked his teacher about his grade. “I gave you a score of 150 points out of 100 possible,??? said the teacher. “What? How can that be???? “Well, I gave you 50 points for disassembling the engine perfectly, another 50 points for reassembling the engine perfectly, and an additional 50 points for doing the whole damn job through the muffler!???