it's a bit harder to know if an older account's Rep is close to being self made or purchased.

The early accounts likely benefited from being early accounts and collecting large amounts of Steem along the way. THis gave them an edge at every step

I am always curious as to why some one ended up in the minus range, and that can take a bit of digging,

Most is for spam or plagiarism, some are automated comment accounts that run through a set of phrases. anything for a dollar, as they say.