The sales man part was really funny.  My mother used to say "quote your source" (she was a pseudo feminist)  So I have taken to ask people who tell me things are "Biblical" to show me where they found "that" in the Bible and then I will believe it.  Usually they can't or won't take the time, but I figure at the very least, if they are really argumentative they will actually try to find it and there for be exposed to something Biblical.  God does promise His word won't return void.  My thinking is that every time I can get some one exposed to His actual words the greater the opportunity for God to bring them into His way of thinking.
 
We are so fortunate to be living in the time we live, to see how alive and real God's Word is, and to witness His hand in all of our lives.  We do serve an awesome God
 
Yours in Christ,
 
Jill