My Mitsubishi was terrible, particularly the transmission, which all but died on me. It was a miracle that the next used car place I went to, where I brought the Mitsubishi as a trade-in, gave me something like $3000 in trade-in credit. I hid nothing, although they didn't specifically ask about the condition of the car. It happened to have new body work because somebody had smashed the side during a hit-and-run when I was inside, on the freeway. (2nd miracle; it was a wonder I didn't end up in the hospital; I was utterly untouched and uninjured.)
Just because they liked the look of it (I think), they accepted it. I asked them if they were planning to resell it; no, they said; they would only auction it off for parts. Clearly they were going to take a loss on it, and it was my down payment on a slightly used Hyundai Elantra GT -- my fake "sports car" that has both manual and automatic transmission. (I know how to drive both, of course.)
There are no secrets these days, I think, at least from our State Department of Motor Vehicles. Every time a car is worked on, including by an independent mechanic, the diagnosis and repair has to be recorded.
I love my little Hyundai; hated the Mitsubishi from the very beginning, but at the time I bought the latter, my credit was lousy and it was all I could afford. I spent years rebuilding my credit, which allowed me to buy the next car because my credit score was something like 770 this most recent time.