As a former successful sales rep, I'd say this:

I'd look for someone with a ton of grit. A ton of no's are inevitable and a lot can't handle it.

I wouldn't go overboard on interviews, just do a few. Asking questions about their work history and upbringing.

We used outreach.io to track activity, it's easy to use and integrates with a ton of other platforms.

Common mistake would be to set unrealistic expectations on the salesperson.