Most things can just be washed, because dangerous bacteria is only present in trapped soil on the surface. Some things need to be examined and have damaged parts/layers removed, like with green onions. Some things can never actually be definitively safe, like lettuce, because they harbor the bacteria inside their leaves (this is why lettuce is the #1 cause of food poisoning by overall numbers, even if there are more dangerous individual foods like oysters).

Then there's pickling and fermenting, which usually makes things much better anyways and which kill off undesirable bacteria by creating a highly acidic environment. For example, raw cabbage isn't great and cooked cabbage is revolting, but cabbage pickled alongside strong aromatics like garlic, onion, and ginger is fantastic.