Don't just scream when things go wrong. Why not acknowledge when things go right? These days, we all can use an "attaboy."
Perhaps the salesperson went beyond the call of duty and offered extraordinary service or maybe it was a small act of kindness.
Beyond thanking the salesperson, take a moment to jot down his or her name. When you get home, call the store. Find out the name of the person's supervisor and the address of the store. Then, write a brief note to the supervisor explaining how the salesperson helped you. Send a copy of the note to the salesperson.
Finally, go out of your way to patronize businesses where you get good service. That will do more to encourage responsive service than complaints ever will.