Site With Quality Issues Switched Domains, Saw Temporary Google Ranking Boost & Dropped Again

On last Friday's hangout with Google's John Mueller, Ankit Dalal, an SEO, asked about a site he is working on and what the issue it has with rankings. In short, the site was not ranking well, so they migrated the site to a new domain and the rankings climbed for a three-day period, then after that, the rankings went back down to where the original domain was ranking.