I've made the mistake of assuming a newbie's plane was fine because I was told "it was previously flown". In the first flight the plane crashed when a linkage pulled out.

As an instructor I considered it MY responsibility to look over the plane and deem it flight worthy. I failed to do so in this instance.

I swallowed my pride and purchased a complete brand new setup for the newbie, even though he did not blame me for his plane's demise.

Bottom line: It need not be "your best friend", just a responsible instructor.