On Sturmgewehr.com and subguns.com, and other forums, REFCHK posting is used for this purpose.
You usually post "REFCHK: full name, state" and people will post/email positive/bad experiences they have had with that person.
Here is a sample post from subguns.com:
http://www.subguns.com/boards/inquir...cgi?read=39913
--John