This article is from the sci.lang.translation FAQ, by James Hester (email@example.com) with numerous contributions by others.
(from replies by Steve Marzuola and Gabe Bokor)
If the suspect company is based in the US, the Better Business Bureau
(BBB) keeps information on complaints against that company. The BBB
will tell anyone who asks (a) whether the company is a member of the
BBB and has promised to abide by the BBB Code of Ethics, and (b) that
the company has XX (number) of unresolved complaints. Most BBBs are
organised by city, not state.
(information from other countries welcome)