Public domain means public domain. There's no restrictions on publishing works in the public domain in whole or in part. There doesn't have to be fair use or anything.
Many public domain works are available for 99c or free, however, so finding unpublished public domain works to make money on (obviously more popular works will sell more) is not exactly easy.
Many public domain works are available for 99c or free, however, so finding unpublished public domain works to make money on (obviously more popular works will sell more) is not exactly easy.