The difference between checking and not checking.

"1" and "looking for receipt" are more formal and polite expressions, which are often used in formal occasions such as letters and official documents. There is a meaning of expecting and asking the other party to receive, which means that the sender expresses his expectation and hope for the other party to receive.

2. "Please check" is more common and is used in informal occasions such as daily letters, emails and text messages. It is a polite request, expressing the sender's respect and courtesy to the other party, hoping that the other party can receive the sent items or information.