Suppose if I buy something from a user in this forum ? And after the transaction and trading am I supposed to ask him to give me a feedback in my profile ?
No, you don't need to ask for it.
how do you see this ?
This should vary from one user to another.
If it were me, I would be happy to give you positive feedback for successful trading without any problems. I consider the risks of trading, and if all of that goes smoothly without any problems then I reserve the right to give you that feedback.