One of Three Basic Research Guides,
It is not a tutorial in how to search public records, but it does includes helpful introductory chapters and the bottom line is that using this book is cheaper than out-sourcing the work, so if you have a need to search public records online, this book is certainly a valuable and cost-effective place to start.
The other two books from the same publisher that I recommend are Find It Online, Fourth Edition: The Complete Guide to Online Research (Find It Online: The Complete Guide to Online Research) by Alan M. Schlein, and Online Competitive Intelligence, 2nd Edition: Increase Your Profits Using Cyber-Intelligence by Helen Burwell, the Grand Dame of global information brokering who for many years published the absolutely top-notch Burwell World Directory of Information Brokers (I have the 1998 edition and it is still useful to me).
The New Craft of Intelligence: Personal, Public, & Political–Citizen's Action Handbook for Fighting Terrorism, Genocide, Disease, Toxic Bombs, & Corruption
Information Operations: All Information, All Languages, All the Time