Food safety’s a difficult thing. When it comes right down to it, just about everything you put in your mouth has the potential to make you sick. We like to think that meat is the real bad thing, but it’s not - you can easily get sick from contaminated vegetables or fruits.
The best thing you can do is to cook everything, but even that’s not 100%. Not all baddies are killed by heat. Botulism, for example, will still be plenty able to hurt you no matter how hot it gets. And who the heck wants to cook their lettuce or other fresh veggies/fruit?
On the other hand, we’re all here, and we all eat everyday. So though the chances of getting sick are there (we’ve all experienced it) it’s typically not frequent enough or bad enough that most of us want to take every precaution there is.
So just use common sense. That fully-cooked sausage, if it’s been stored correctly, is no more likely to hurt you than the raw carrot in your salad. Can they hurt you? Sure. Everything can. But when it comes right down to it, there’s not much you can do to be 100% sure you’ll never get food poisoning.