Perhaps it's the police responding to adds on QLD as it's not legal to sell (or even give away) powder, primers or ammunition here unless you have a dealer license.
If they do get in first they get an easy firearms related conviction and to take somebody's license and guns away.
I thought they were all dealer ads for that reason. Would have thought it any private sales were being repeatedly grabbed by police the sites wouldnt be approving the ads going up?