I run trips and guiding out there. All the shuttle services out there include guides. The bulk of the land used is private. Agreements are in place between landowners, authorities and CIPS (Comitato Independente Pulizia Sentieri), the guys who build and clean the trails, and money raised though the 45 Euros per day shuttle payment also goes towards CIPS. Without them there would be no trails to ride, simple.
People do however try and go it alone, run their own shuttles even and are basically sticking 2 fingers up to the volunteers that make the fantastic riding there possible. CIPS offer a 50 Euro sticker for your car that is valid for a year. I work with EZE Freeride when I do my trips, Enrico from EZE is the President of CIPS. We have seen groups of 10 riders turn up, ride all day, and refuse to cough up 5 euros each for a years pass… price of a beer.
Do you need a guide? IMHO Yes, it’s a labyrinth up there, nothing is sign posted and you are supporting the infrastructure there. I am running 2 weeks in October there around the EWS event and possible another week or 2 in June/July. http://www.rebbens.info has some basic information.