I think you should focus on things you can enforce. For example, in Austria companies are required to provide certain information in job ads (eg. salary range,

I think you should focus on things you can enforce. For example, in Austria companies are required to provide certain information in job ads (eg. salary range, weekly hours, type of contract) and it's trivial to enforce because you can see if the information is there or not. I'm not sure if it helps with ghost job ads, though.