How to find out that the user has received the product?

Question

PHP

Hello.
A question.
How to properly organize this system?
For example, one user has a product, he wants to sell it and puts it on the site, another user buys his product, but how do you know that the user received this product?
It's just that the first user can say that he sent the product but did not actually send it, and the other one can say that he did not receive anything, although he actually received it.
Thank you.

Answer 1

This is all based on trust. Of course, you can look at postal tracking, but this is not reliable. Or delivery like DHL.