Before buying a link from a site, or buying an expired domain, I always look it up in the Wayback Machine.
– See if it was a real site or a spam / casino / pharma page before
– Spot sites that suddenly changed niche (common with link farms)
– Recover old content from your own site after a bad migration
Also use it to see if a link-selling site’s content quality changed. If a site went from real articles to “write for us” everything overnight, skip it.