Expired Domains for SEO and private networks is still a very strong strategy that is very much still alive. It's important that the domains are clean and don't have any questionable history, along with having a lot of links from strong sites.
Checking for spam in wayback machine is the stage where we filter most of our domains out.
However you purchase from, you need to ensure they do their due diligence and only charge you for domains after they deliver in full.