What things must one keep in mind after buying a flat?

I want to know this because one of my cousin bought a 1 bedroom flat in Mumbai. What should he be aware of ? Does he have to arrange any lawyer ?

Kindly advice what is most important for him so that he will be aware of not being cheated in any case, by anybody.

I don’t have any knowledge, so I would like you to please help him out.

Thank you.