My experience is that it differs from client to client.  I've learned to read their personalities a bit and THEN show the homes accordingly.

I also think there's a difference between showings that take place when you have no idea what they will ultimately buy in the beginning, when the appointments are almost like mini crash courses in what it will take to wow that particular client.  After a few showings and alot of dialogue, I can usually cut showing times much shorter because I know the minute we walk in whether or not something will work.

I think it's about communication....I once had a gentleman that even though he said "this is not for me" all the way through the house, he still felt the need to view the whole thing out of courtesy to the seller....including examining the furnace and other mechanicals.  I let my people know right up front that I want to hear what they REALLY think right up front!  The more verbal they are the easier the process is.