Ask HN: Refundable deposit in an app a good idea?

Does anyone have experience using refundable deposits to filter out serious applicants/users from not-so-serious ones? Does it work? Why or why not?

An example of a service that uses refundable deposits is Crew (https://crew.co). After submitting your project specs to them, they ask for a refundable deposit to gauge your level of intent before making introductions.