This doesn’t have to be a full-blown CRM system. A simple database that you keep up-to-date with contact details and what they bought will suffice. CRM can come later.
Keep in touch
I’ve given some hints earlier, like email updates / newsletters for example; and solicit feedback from customers on how you can do better.
So, there you have it. Awesome customer service is king, and there are many ways to achieve it.
“If you were to ask me to name three geniuses, I probably wouldn't say Einstein or Newton…
... I'd go Milligan, Cleese, Everett, Sales Funnel Man..." (OK, I added the last one)