This might fix it: charge the candidate some $amount for each application they send. Also charge the employer $amount * some_factor for each application they receive.

This can filter out candidates that aren't really interested, and companies that aren't really hiring.

The cost to an employer to accept (not review) 100 applications is about 1/100th of the cost to the candidate.

Employers have more information about the applicants individually and in aggregate but candidates don't about the companies.

Employers don't give much basic feedback to candidates, like underqualified, overqualified, not sure, something else.