I hate it when you have to give up on a client just so he can state he is right (although he/she is so so SOOOOO wrong) before leaving (usually without purchasing anything).
This happens a lot in my work place, say today; A client asked me about a specific game which its release date is still unknown as of today. The client kept on rambling that he's 100% sure that the game is out (damn you teasers!) and he was not determined to leave until I agreed with him. I have proof, I know I'm right but I also know things could get worse if I disagree, so eventually...
...I give up and let him win... again :(
I hate it!