You cannot be disappointed if you have no expectations against which you’ve plotted your hopes. Setting expectations can help you close a deal with a new customer or please an existing customer. But always engineer customer service expectations for success.
Keep expectations reasonable. Don’t over-promise with good intention—if there is a risk of not delivering. Don’t under-promise based on weak assumptions of what you can deliver—low standards can be the beginning of the end in a customer relationship.
When setting expectations, either end of the spectrum (low or impossible expectations) will erode trust between you and your customers. Over-promising and delivering seems like an ideal scenario, but also does not meet the customer’s expectations. Occasionally going out of your way to provide exceptional experiences for a handful of customers can be a great gesture; unless your customers are dissatisfied with the level of service they routinely receive. Ensure your day-to-day customer service practices are in line before conquering loftier goals. Cherries on top are always nice, but don’t plant an orchard you can’t maintain.
On the other hand, intentionally under-promising to give the appearance of greater value is a risk as well. Giving your customers a positive experience is a part of the role of any good customer service agent. Denying them that experience so you can come back and save the day for them is a cheap way to impress people, who will no doubt eventually catch on that you are manufacturing problems to seem like a hero.
Be reasonable with your customers, and set their expectations with reality. Keeping yourself insulated against further customer disappointment can only happen if everyone is on the same page.