Hah yeah I missed such a customer too. I was done with the sword, but they were out of the room. I got sad and waited for a customer, but noone came. So I went out looking for them. The same customer was standing around next to my house, around the corner.
Due to their alignment AWAY from my house I thought "hey maybe it's that last customer" - and yes I could just push my sword in their face and it unfroze the game :D