Every customer is a member.
At least, that's an argument I've tried to make a couple times here. To me, "customer" implies someone that completed a transaction, while "member" signifies relationship, belonging on an ongoing basis.
Even if your business model is not subscription- or membership-based, you can benefit from that member mindset.
A key function of having members instead of customers? Engagement.
Keeping their attention, and hitting them with the right value and the right touchpoints at the right time.
Keep people engaged, and renewal - or just the next transaction - will take care of itself.
Easier said than done, right?