There are different reasons why a complaint letter is written which is the reason why there are also various kinds of complaint letter formats that can be used. (template.net)
This is perhaps a funny kind of complaint, but I had trouble with this one because I didn't believe it all! (goodreads.com)
There's some interesting information on the volume of particular kinds of complaints by time of day — who would have thought that illegal parking complaints peak at 7 a.m.? (legalblogwatch.typepad.com)