Not only does this disincentivize HR from running fake vacancies or stringing multiple candidates on just to keep their options open, but it also solves the problem of unemployed people job-searching effectively working full-time for free. The fact that companies would have to pay to hire workers would mean they try to make the selection as short and effective as possible.
Ah, so you are thinking there would be a centralized system to track applicants* (perhaps the same one that handles payment) - this sounds feasible, the infrastructure mostly already exists (in the US) in state unemployment departments.
*(without it centralized, each company only sees a person once and doesn’t know if they accepted another offer or whatnot)
The rest of your points are also good, I don’t actually think it would be a big issue, I just had the knee jerk reaction to think about how any good idea would fail these days.
A half dozen applicant tracking systems handle 90% of the jobs that require interviews.
You could probably do a professional interviewer job for something like restaurant work in a major metropolitan area (but restaurants probably won’t do this and would just start hiring through referral or from resumes instead), but most industries are small enough that companies would talk. I haven’t worked in my previous field for five years, but checking now, I still know people at all of the major companies for it. If I were to apply at any of them, someone would see that I’d worked at companies X and Y, then they’d ask all of the people at their company who’d previously worked at company X or Y, to see if anyone knew me. If I were to try to be a vocational applicant like this, I’d develop a reputation pretty quickly.
Companies would just get even more suspicious about long resume gaps or people trying out a new field.