Who determine the depreciation of cars? Is there any formula? Which brands have better retained values?
The used car market does - what people are willing to pay for something and the available inventory. The more cars of a particular model there are and with fewer buyers, the lower the price. A model or mfr's reputation also as a lot to do with what people will pay. Kinda like the stock market.
I buy all my cars used. Let the first fella take the depreciation. And work all the kinks out. I used to buy cars when they first came out. Then I wised up.