How do I know if an office product is real or not? I mean is it pirated or is it authentic. Is there some way I can tell before I purchase the product?

Secondly, does a disk generally come with the purchase or is it download only?

Basically I want to buy a 2016 or 2019 but there are so many difference choices with prices ranging from under $10 to over $150. So how do I tell if the product is authentic or not?