Very disrespectful and unprofessional. The COO (acting as the recruiter I guess) emailed me asking for my availability for a phone interview. After 3 weeks of emailing and bouncing dates to chat (as he took a week to answer each message), he finally picks a schedule that he never confirmed back (to be fair). On that day I waited for his call but it never came. Messaged back (twice) to ask about that and never received any reply! I can understand you can be super busy but answering people you messaged in the first place, is the bare minimum in a professional environment. If you don't have time, hand the task to others who have. If you are not interested in a candidate anymore let her/him know; candidates have jobs and lives too and nobody wants to waste time waiting for nothing.