They give you the first (and maybe the second) book of a series and hope that you will buy the rest.
Very cool! Thank you.
Many of Baen's hardbacks come with a CD of the eBooks for all previous books in the series. No DRM. Instead they have a very polite request asking you not to post on line.
To what Emily has added to this thread.
Note, that even with the very polite request, the CD's are readily available on-line.
Thank you for your patience