Ask HN: What are the biggest challenges preventing startups from hiring remote?

We're starting a new company focused on solving the problem of talent war by helping late-stage startups have successful remote collaborations with tech talent. However, we're still trying to figure out which vertical to focus on. Which of these verticals is most pressing?

1. Sourcing & vetting candidates? 2. Managing international payroll? 3. Bootcamps? 4. Infrastructure & working space?

Let me know your thoughts!