It sounds better in the singular to me as a single thing is sold. In other sentences, as a BE speaker, I'm happy with either.
So if it sounds ok then it must be ok? The answer to all of these types of questions is easy. How many of the things are involved? In this case it's ONE company.
company is a singular different entity altogether as per law, so cannot be sold as "are".
If you sell the people who work there, it's "are" :)