I believe HN is a high quality forum that enforces high quality standards, there is no reason this shouldn't be a thing. Companies that advertise here should be held accountable.
I expect YC to do due diligence if one of their companies receives several reports that they heard no replies (it's not that many companies). If it's found to be more than hearsay, they lose HN ad privelleges.
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I wouldn't do a startup but I certainly could see myself creating a bunch of fake developer profiles of varying skill levels and sending them to companies en masse. If they don't reply to anything even though they have had a job opening, they get placed on the (public) name & shame list.
Would also be interesting to automatically keep track of which job openings a company has and how long they've been open for.