Do I end a Complain letter of complaint with 'Yours sincerely' or 'Yours truly' or 'Yours faithfully'? Or something else?
You'd end the letter with 'Yours sincerely' or 'Sincerely' if you know the person who you're addressing it to, for example, Dear Mr Smith, Dear Ms Hill. 'Yours faithfully' when you do not know the person who you are writing to - Dear Sir/Madam, Director of... etc. 'Yours truly' seems a little unusual for closing a letter of complaint. I'd stick with either of the first two.