I think that it is not fair only pointing out opponent’s drawbacks. In advertisements, they should appeal that something like “I were you, I would do…” It is not fair only criticising opponent without mentioning about yourselves. Criticising does not necessarily mean your are better than your opponent. On the other hand, audience should have ability that they can criticise advertisements so that they can judge an advertisement is negative advertisement or not.
To create efficient advertisements, it is important to do a lot of research beforehand. Since when it comes to political advertising, they tend to don’t have long time till deadline.