Yes, prepayment penalties are a thing. But every time this comes up, we see reports of too-good-to-be -true deals that don't have them. See, for example, this thread:

https://news.ycombinator.com/item?id=14484615

I also had a friend do exactly what I described, and there was another thread where they only had to make two payments and then could pay off the rest without penalty (and even that was an unspoken gentlemen's agreement with the dealer) -- will find if I get a chance.

The point is, it's simply not warranted to assume as a bedrock of truth that no dealer every makes a confused deal in this respect, as chrisseaton was insisting.