You may block, unblock or even report a buyer/seller anytime inside the app.
To do this, go to their profile and tap on the 3 dots in the upper right corner and select 'Block/Unblock this Person' or 'Report'.
Additionally, you may want to leave a review about your experience - especially for repeat offenders.
To do this, open the conversation window and click 'RATE' on the upper-right corner.
From there, you can select the rating according to your experience and leave any comments in the text box below.
Remember to click Send when you're done!