Based on prior knowledge, it can be assumed that the safety feature of a car is an important factor in determining the decision to buy the car. In general, cars with higher safety ratings are more likely to be rated as "good" or "very good" in terms of the decision to buy, while cars with lower safety ratings are more likely to be rated as "unacceptable".

Here is the generated dictionary based on the relationship between the safety feature and the decision to buy:

```json
{
	"unacceptable": ["low"],  
	"acceptable": ["low", "med"],
	"good": ["med"],
	"very good": ["high"]
}
```

Explanation:
- Cars with a safety rating of "low" are more likely to be rated as "unacceptable".
- Cars with safety ratings of "low" or "med" are more likely to be rated as "acceptable".
- Cars with a safety rating of "med" are more likely to be rated as "good".
- Cars with a safety rating of "high" are more likely to be rated as "very good".

Note: In this particular case, it is assumed that there are no hard-to-predict safety values, and the possible values of the safety feature are ['low', 'med', 'high'].