You can’t say “Party X just wants your money”, try “Our party will help you keep your money”, or even “Unlike some parties today, we will put your taxes to good use”.
It’s a lot harder to make a compelling attack without a concrete focus. “Some parties are corrupt” is so trivially true that’s it embarassing, but “Party X is corrupt” is a rallying cry.
It won’t prevent lies by any means, but since specific claims can only be nade about your own party it gives an advantage to talking about your own party instead of every ad being incredibly negative claims one step off of a flame war. Hopefully that leads to building a strong case and then defending that case during debates, but at least the ads will have less direct negativity.