If a customer has bought from you once, even if they had a bad experience, you can still get them back. More importantly, you need to find a way to do it! Customers who have had bad experiences will talk to others.
This is a huge area for improvement for all salespeople. As good as anyone may think they are, I have yet to find someone or some company that does such a good job that an old customer doesn’t slip through the cracks. In reality, for most salespeople there are customers who quietly fade away, not because they weren’t happy, but because the salesperson merely failed to remain in contact. Over the years of my work with hundreds of salespeople, I’ve come to believe there is at minimum a 10% increase in sales that could be obtained by doing a better job of reaching out to lost customers. Now, I don’t know of too many salespeople who couldn’t use a 10% increase in sales! No matter how old or lost you may feel the customer is, there’s no better time than right now to start reaching out to them.