UPDATE: Looks like Craigslist has documented this info here. The info below is no longer accurate.
There are several tricks for creating more powerful, focused searches on Craigslist.- The NOT search - placing a dash "-" in front of a search term will exclude items that include that word. So if you're shopping for a car and you want to look at Hondas but you don't like Civics you can search for "honda -civic".
- The OR search - placing a single quote in front of multiple terms will search for items that include any of the terms. Craigslist searches are by default AND searches - that is an ad has to include all of the entered terms to turn up in a search. So if you want to search for Civics or Accords you can search "'civic 'accord".
- Combined AND/OR searching. Parentheses can be used to combine two OR searches. So if you want either a Honda or a Toyota, but you only want to see newer models you can search "('honda 'toyota) ('2005 '2006)"