Reality is different. I do not understand why people look for without registration ad posting sites. Most probably you will do some illegal work otherwise your purpose may be blackmailing. Mostly this is considered as spam. There are hundreds of free classified sites. You have to just sign up once and start posting ads. One thing is sure there is spam.
Today I decided to make a search on free ad posting sites that does not require signup. No any of these sites are popular; no any of these sites has good rank. No any of these sites have potential.