Hello, 3dyx! What you are saying is right. Without a regulated control from a third-party, price of the cars may fluctuate. What is important to note, though, is that the current centralized market has no control over the credibility of provided information - we get fraudulent deals, unacceptable rates, and 'lemon cars' happen more often than we want. If, however, we only had comparable size of car data uploaded to the blockchain network, be it six months' or an year's worth of accumulated information, the transparency in the information that we would get will be unmatched to what we are given right now.
Part of what we plan to achieve is to make it so that the car owners may have the option to choose whether to have third parties (repair shops, maintenance centers, insurance companies, etc) upload their car history to the network or not. Since it is not an intermediary uploading the data, the information will have higher credibility than what we get when we ask about a car at a dealership. This is one of the main belief; that ultimately, drivers all around the world will benefit from the clear, transparent car data.