The wife card has been played with me by aspirant buyers about half a dozen times. Guys that are absolutely 100% positive that they want to and will buy a machine. Only to cancel the deal a few days later, because 'the wife doesn't agree with another machine'.
I don't like it at all. I find it weak when people don't stand for their agreements without any good arguments. If you're so sure you'll buy my machine, I am assuming you've spoken to your wife about it BEFORE you make the agreement with me.