1. It depends on how desperate the applicant is: if they're searching while still employed then they can walk (like GP did).
2. Even if they are desperate, they may take the offer… for now… so they can start getting a salary again, but that won't prevent them from continue to look. In which case you're paying for them to learn a job which they'll leave and you'll have to pay someone (else) a second time to learn as well.
False economy IMHO.