Getting input on UI

Most of the developers on my team likes getting feedback from users about usability and functionality but I've found a problem. I probably do the same mistake. Let's say you have a new function for registrating costs. What's the difference between these two scenarios:

1. Developer goes to user and shows the new functionality and the user gives feedback.
2. Developer goes to user and asks him to register a new cost.

The difference lies in the response: in the first case the user gives response to the developer's demo. In the other case the user tests if he can use the functionality.

In real life for the real user, there will be no developer doing the chores. The user have to do it himself. So, of course the second method is preferable. If your expert users cannot find their way around the UI, how will the ordinary user do?