Who is responsible to check if a tax sale case is valid

[Jianzhou Zhao]

Can we assume all listed tax sale (tax lien, tax deed or hybrid) properties are valid cases?

For example, I found some properties are owned by non-profit companies exempted from property taxes, and a property has non-paid tax because the property address was changed (for example, the street or the city name is renamed) while for some reason its county still uses the previous address to collect tax... I can imagine there could be other cases I do not know based on my knowledge.

If I won tax sale for such cases, what would happen? Will such property owners still need to repay me? Will county refund my purchase cost?