Everyone wants their customers to come back, buy more of the stuff they are selling. Getting repeat business isn't that easy though because there obviously are other people selling the same products and services as you.
In order to get your customers to keep coming back, you should get their feedback and use it to improve your business.
While you may be sure that your customer service is great, you sell high quality goods and so on, maybe your customers want more? And how do you find out if they do? Ask for their feedback regularly and give them what they want.
If you listen to your customers, they'll know you value them and they will be back to buy more of your products or services.