You can use archive.org to rebuild the previous content of the site. Can be tough sometimes because there will be missing parts of the site, missing parts of articles, etc. Also you might get into legal trouble if the previous owner finds out you copied his content (for small to medium sized sites I guess that isn't much of a concern.. it's pretty expensive to sue random people who might not even have any money to go after.. worse case you get a DCMA and you take the content down.)
Make sure to check if the content hasnt been copied from other webmasters.. I've done that a lot with my foreign language sites.