Here's one way to address the problem of ghost jobs using taxes:
Force every job post to include a salary range. Make companies pay a small "job posting tax" for every listing, which is proportional to the product of the job's stated salary, and the number of views or applications it gets.
Including a salary range in every job will improve gender equality and help jobseekers save time.
The nominal "job posting tax" should aim to be a small fraction of the actual cost of making a new hire (say 1-5% of the equivalent labor cost for all the work that goes into filling a role). The tax needs to stay small, so companies aren't seriously discouraged from hiring. (Heck, you could even have the tax automatically get reduced a little bit if the economy is in a recession -- or automatically go up if data analysis determines there are too many ghost jobs. Or even refund some taxes once a hire actually gets made!)
The goal is just to apply some financial drag to companies that spam job listings. If you're inconveniencing jobseekers, you've got to pay a little tax for it. Identify the right tax scheme and everything should sort itself out.