misleading and vague subject lines - "I need help .... " with what??
people responding to a "wanted" with "I don't have it" and no useful suggestion as to where it might be found
asking for an item after it is no longer available - when "Sold" is in the topic line
unconventional spelling - but maybe that's the best the writer can do - I try to go for the content on those
really long paragraphs - I find them hard to read and understand