I dont think the post by OhThatPatrick explains the jist of this problem.
The most important detail in the stimuli is "each person who bears the risks"
I dont think A should be eliminated because it doesn't involve life risks. I think it should be eliminated because older cars without certain safety feautures pose life risks not only to the sales person himself, but also to pedestrains/other drivers, and therefore requires voluntary consent from all these people (basically everyone he could meet on the street while driving his car）as well. Imagine this: an updated safety feature makes sure that the car can brake on time on slippery roads, the lack of which could very easily cause a collision with another car on a rainy day.
D is similarly wrong because "all users of motor vehicles‘’ doesn't cover the full scope of people that might be affected by emitted pollusions. Think pedestrains that don't drive cars, they are bothered by air pollusion as well.
Contrast A, D with C. The fatal injury incurred by lack of helmet only affects the motorcyclist himself, so voluntary consent from him alone is enough to make this acceptable.