The last interaction
Marketers (and high school kids) focus a lot on the first date. After all, you never get a second chance to make a first impression.
I recently had some waterproofing done in the basement. The first date was great. The company was professional and had every single element down, from their AdWords to the web site to the way they interacted on the phone and in person.
I think that stuff is pretty important, but I'm way more interested in the last interaction than I am in the first (and if you care about word of mouth, you should be too).
After they finished the job, they left my basement a mess.
Forever, my only memory of the job is going to be the mess. Forever, the only thing I'll talk about is the mess. The last interaction, in my experience, is responsible for virtually all of the word of mouth you're going to get, positive or negative.
That free muffin at the restaurant or the lollipop at the barber or the call from the Realtor a week after the house is sold and contracts are signed and the movers have left... believe it or not, it matters.
PS The waterproofing guys took the time to call me before I did this post, and that call led to a new last interaction... my bad feelings are already fading, because they stepped up and took action. More proof that it matters.