I bought onions from a truck passing the streets in Mexico and even after peeling the onions smell like manure all the way to the core.
Is this normal? If so, why don't grocery store onions have that smell?
Toss those. That does not sound normal at all. But, possibly, ask someone else to smell them as well.
I'd say it's not normal. The field the onions were grown in probably were fertilized with (too much) manure. I'd throw the onions away.