I think that's a little simplistic. If someone fails to follow through on an agreement to trade and receives their part of the deal without returning anything and then refusing to communicate on the issue, then yes, negative feedback is called for, and if this behaviour becomes a habit, there should be more done than just feedback because not everyone bothers to check the feedback, or even knows how when they first get here. If some are allowed to continue this habit of taking without giving, why should they be allowed to continue with such behaviour. I'd actually like to see something like a "red flag" on their id or account after accumulating a certain number of negatives in a certain time period, just so that people could be forewarned, but this is likely something that isn't feasible, so checking feedback and leaving appropriate feedback is about the only thing that can be done. Being able to contact those who left the negative is also good to find out if it was resolved.