"When a sale is complete, too often I feel like the customer is disappointed with the results. Do they expect too much or is there something wrong with the way I'm handling pre-sale expectations?"
With unmet expectations, the more complex the sale, the louder the customer screams. This belies the myth that "any sale is a good sale." Prevent the "mutual mystification" that frequently builds expectations that cannot be met and causes misunderstandings that are difficult to forget. You will acquire the skill to differentiate between needs and expectations and how to bring them into sync. The end result is eliminating surprises and disappointment for you and the customer.