AVGAS refinement is really not that more controlled than car fuel. Different dye, TEL additive, tested at regular stages. However the big difference is its a limited run specialty fuel. So it's more expensive. High perfromance car users used to sneak some from aircraft bowsers as there was less tax making it cheaper than specialty racing fuels that were more expensive for the same reason. There used to be enough demand for several refineries in Australia, now only the one refinery provides AVGAS. Funny for ages they still had green and blue fuel, which were both the same product with different dyes for retail purposes, the green dye fuel having stuffed up in 2001 which created problems for brass parts in fuel lines and carbys. They conned a lot that the green fuel was still 100/130, but was just BP/Mobils version of 100LL. It was even worse when it was coming from the same refinery in different colours.