Need help understanding competitor tactic

I noticed a guy dominating his niches by simply buying expired sites or domains, turning them into blogs and getting link juice from them. I have been out of BH for a few years doing WH and I'm surprised as to why and how this works. Can someone please help me out by analysing his backlinks? Are the sites expired domains or used sites and why do they retain link juice passing capability? Where can I buy sites like those? I am not going to post urls here but you can pm me to get the list.

just type in google "expire domain" and have fun)

I always thought that changing domain ownership would "reset" it and remove all link juice. Is there a trick then? Using the same IP or same whois privacy service?