How to safely sell iOS apps to another person or entity?

Question

Freelance

Actually, the question is the following. Sometimes they offer to sell their applications for a certain amount.
How to do it correctly and safely. The scheme is as follows, transfer to the buyer's account, then money, then the source code.
Everything seems to be logical, an application without source code is not particularly useful, but, nevertheless.
I would like to know from those who sold or bought applications is this a normal practice and how it usually happens. Firstly, it's interesting, and secondly, I don't want to be thrown if I ever get ready for sale.

Answer 1

Through the corresponding exchange, for example https://www.flippa.com