How do I know if the user is a customer?

WordPress have role and permission system, WordPress have following built-in roles

1 Admin privilege’s 10.
2 Editor
3 Author
4 Subscriber

The Subscriber is consider as client, i mean users, you can made check on this.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)