Carsten, I believe you are a vendor starting a company that will sell services to dealers. That is a challenging endeavor, however franchise dealers are willing to give vendors a chance to prove themselves and sign up for a few months. OEM's would never do that.
I would also caution that dealers will quickly sniff out vendors who they may perceive as having an anti-dealer mentality, why would they want to partner with someone that they feel is rooting against them? Not saying you are, but just something to be cognizant of.
Over the years, dealers have seen hundreds, if not thousands, of vendors enter the automotive retail space with a technology background and venture capital $ looking to disrupt how business is done. The vast majority fail. The ones that succeed are the ones that bring in talent with dealership experience.
It has to be a blend of technology + automotive retail experience. Tekion is a great example. Their CEO, Jay Vijayan, came from Tesla. He has created an absolute innovative disruptor in automotive retail, but they are adapting their business to fit dealerships' needs. He even bought 2 stores of his own to learn first hand. This is the formula for success.